Reception device and reception method

ABSTRACT

A reception device includes: a receiver that receives a multiplexed signal; a first demapper that demaps the multiplexed signal, with a second modulated symbol stream of a second data series being included in the multiplexed signal as an undefined signal component, to generate a first bit likelihood stream of a first data series; a second demapper that demaps the multiplexed signal, with a first modulated symbol stream of the first data series being included in the multiplexed signal as an undefined signal component, to generate a second bit likelihood stream of the second data series; a first decoder that performs error control decoding on the first bit likelihood stream to derive the first data series; and a second decoder that performs error control decoding on the second bit likelihood stream to derive the second data series.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. continuation application of PCT InternationalPatent Application Number PCT/JP2017/011679 filed on Mar. 23, 2017,claiming the benefit of priority of Japanese Patent Application Number2016-069578 filed on Mar. 30, 2016, and Japanese Patent ApplicationNumber 2016-254546 filed on Dec. 27, 2016, the entire contents of whichare hereby incorporated by reference.

BACKGROUND 1. Technical Field

The present disclosure relates to a reception device, etc. that receivea multiplexed signal and derive a plurality of data series from themultiplexed signal.

2. Description of the Related Art

A multiplexing scheme utilizing superposition coding is known as ascheme to multiplex and send a plurality of data series (see SeokhyunYOON and Donghee KIM, Performance of Superposition CodedBroadcast/Unicast Service Overlay System, IEICE Transactions onCommunications, vol. E91-B, No. 9). Other known multiplexing schemesinclude time division multiplexing and frequency division multiplexing(see Thomas M. Cover, Broadcast Channels, IEEE Transactions onInformation Theory, vol. IT-18, No. 1).

Compared to time division multiplexing and frequency divisionmultiplexing, the multiplexing scheme utilizing superposition coding issuited to multiplexing a plurality of data series that are required tohave different levels of noise tolerance (receiver tolerance). Themultiplexing scheme utilizing superposition coding is also termed aslayer division multiplexing. The multiplexing scheme utilizingsuperposition coding applied to multiple access is also known asnon-orthogonal division multiple access (NOMA).

In the multiplexing scheme utilizing superposition coding, atransmission device superposes a plurality of modulated symbols, whichare obtained by modulating each of a plurality of data series, usingpredetermined power allocation, and transmits the superposed modulatedsymbols. A reception device sequentially demodulates the modulatedsymbols that are multiplexed by superposition coding, starting withmodulated symbols in a layer with high noise tolerance until thecompletion of demodulating modulated symbols in a layer to which adesired data series belongs.

More specifically, the reception device demodulates the modulatedsymbols in a layer with the highest noise tolerance to estimate a dataseries. When a desired data series is yet to be estimated, the receptiondevice generates a replica of each modulated symbol from another dataseries that has been estimated to cancel the replica from the receivedsignal, and demodulates modulated symbols in a layer with the secondhighest noise tolerance to estimate another data series. The receptiondevice repeats these processes until the desired data series isestimated.

SUMMARY

In some cases, the multiplexing scheme utilizing superposition codingfails to efficiently process a plurality of data series.

For example, the multiplexing scheme utilizing superposition coding issubjected to processing delays due to the process that requiressequential decoding of a plurality of multiplexed data series.Furthermore, the multiplexing scheme utilizing superposition codingrequires the reception device to include an arithmetic resource, etc.for re-modulating a forward decoded data series. The reception device isalso required to include a memory resource, etc. for holding receivedsymbols used to decode the subsequent data series, from when theprevious data series is decoded and re-modulated until when a modulatedsymbol stream of the previous data series is obtained.

Moreover, the multiplexing scheme utilizing superposition coding maysuffer a decrease in transmission capacity due to a plurality ofsuperposed data series affecting each another.

The present disclosure provides exemplary embodiments that solve theabove-described problems involved in the multiplexing scheme utilizingsuperposition coding. The present disclosure, however, also provides anaspect that solves not completely but partially the above-describedproblems, or an aspect that solves a problem different from theabove-described problems.

The reception device according to one aspect of the present disclosureis a reception device that receives a multiplexed signal into which aplurality of data series have been multiplexed by superposition coding,and derives the plurality of data series from the multiplexed signal,the plurality of data series including a first data series in a firstlayer and a second data series in a second layer. Such reception deviceincludes: a receiver that receives the multiplexed signal; a firstdemapper that demaps the multiplexed signal, with a second modulatedsymbol stream of the second data series being included in themultiplexed signal as an undefined signal component, to generate a firstbit likelihood stream of the first data series; a second demapper thatdemaps the multiplexed signal, with a first modulated symbol stream ofthe first data series being included in the multiplexed signal as anundefined signal component, to generate a second bit likelihood streamof the second data series; a first decoder that performs error controldecoding on the first bit likelihood stream to derive the first dataseries; and a second decoder that performs error control decoding on thesecond bit likelihood stream to derive the second data series.

Note that these general or specific aspects may be implemented as asystem, a device, a method, an integrated circuit, a computer program,or a non-transitory, computer-readable recording medium such as aCD-ROM, or may be implemented as any combination of a system, a device amethod, an integrated circuit, a computer program, and a recordingmedium.

The reception device, etc. according to one aspect of the presentdisclosure are capable of efficiently performing processes in amultiplexing scheme utilizing superposition coding.

Further merits and advantageous effects in one aspect of the presentdisclosure will become apparent from the following description anddrawings. These merits and advantageous effects are provided by thecharacteristics described in the following description and drawings.However, not all of these merits and advantageous effects are requiredto be provided, and thus one or more of these merits and advantageouseffects may be provided by one or more of the characteristics describedin the description and drawings.

BRIEF DESCRIPTION OF DRAWINGS

These and other objects, advantages and features of the disclosure willbecome apparent from the following description thereof taken inconjunction with the accompanying drawings that illustrate a specificembodiment of the present disclosure.

FIG. 1 is a block diagram of an example configuration of a transmissiondevice according to Embodiment 1;

FIG. 2 is a block diagram of an example configuration of a receptiondevice according to Embodiment 1;

FIG. 3 is a diagram showing transmission capacities in superpositioncoding;

FIG. 4 is a diagram showing an example QPSK constellation;

FIG. 5 is a diagram showing an example non-uniform constellation;

FIG. 6 is a diagram showing transmission capacities in superpositioncoding using QPSK and Nu-256QAM;

FIG. 7 is a block diagram of a first example configuration of areception device according to Embodiment 2;

FIG. 8 is a diagram showing an example superposition constellation;

FIG. 9 is a flowchart of a first example of reception operationsaccording to Embodiment 2;

FIG. 10 is a diagram showing an example result of simulation to comparesequential decoding and parallel decoding in superposition coding;

FIG. 11 is a block diagram of a second example configuration of thereception device according to Embodiment 2;

FIG. 12 is a flowchart of a second example of reception operationsaccording to Embodiment 2;

FIG. 13 is a block diagram of a first example configuration of atransmission device according to Embodiment 3;

FIG. 14 is a block diagram of a second example configuration of thetransmission device according to Embodiment 3;

FIG. 15 is a block diagram of a third example configuration of thetransmission device according to Embodiment 3;

FIG. 16 is a block diagram of a first example configuration of areception device according to Embodiment 3;

FIG. 17 is a block diagram of a second example configuration of thereception device according to Embodiment 3;

FIG. 18 is a block diagram of a third example configuration of thereception device according to Embodiment 3;

FIG. 19 is a block diagram of a fourth example configuration of thereception device according to Embodiment 3;

FIG. 20 is a diagram showing an example of a variation superpositionconstellation according to Embodiment 3;

FIG. 21 is a flowchart of an example of transmission operationsaccording to Embodiment 3;

FIG. 22 is a flowchart of an example of reception operations accordingto Embodiment 3; and

FIG. 23 is a diagram showing an example result of simulation to comparesequential decoding and parallel decoding in a variation ofsuperposition coding.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following describes in detail the embodiments according to thepresent disclosure with reference to the drawings. Note that thefollowing embodiments, etc. show a comprehensive or specificillustration of the present disclosure. The numerical values, shapes,materials, structural components, the arrangement and connection of thestructural components, steps, the processing order of the steps, etc.shown in the following embodiments, etc. are mere examples, and thus arenot intended to limit the present disclosure. Of the structuralcomponents described in the following embodiments, etc. structuralcomponents not recited in any one of the independent claims thatindicate the broadest concepts of the present disclosure will bedescribed as optional structural components.

Also note that encoding may mean error control coding. Error controlcoding is also referred to as error-correcting coding. Also, decodingmay mean error control decoding. Error control decoding is also referredto as error-correcting decoding or error correction. Also, unknown maymean undefined, and transmission may mean sending.

Embodiment 1

The present embodiment describes multiplexing a plurality of data seriesonto a plurality of layers by a multiplexing scheme utilizingsuperposition coding, and transmitting the multiplexed data series.

To simplify the description without loss of generality, the presentembodiment and other embodiments describe an example in which two dataseries are multiplexed onto two different layers to be transmitted.However, the multiplexing scheme described in the present embodiment andother embodiments is applicable to three or more data series multiplexedonto three or more different layers to be transmitted.

Also, the present embodiment and other embodiments use a first layer towhich a first data series belongs as a layer with higher noise tolerancethan a second layer to which a second data series belongs.

FIG. 1 shows an example configuration of transmission device 100 thatmultiplexes two data series onto two layers by superposition coding, andtransmits the multiplexed data series. The configuration and operationof transmission device 100 will be described with reference to FIG. 1.

Transmission device 100 includes encoder 111, interleaver 112, mapper113, multiplier 114, encoder 121, interleaver 122, mapper 123,multiplier 124, adder 130, and radio frequency unit (RF unit) 140. Thesestructural components may also be implemented as dedicated orgeneral-purpose circuits. Multiplier 114, multiplier 124, and adder 130can also be represented collectively as a superposition unit. RF unit140 can also be represented as a transmitter. RF unit 140 may include anantenna.

Encoder 111 encodes an inputted first data series on the basis of afirst error control coding scheme to generate a first bit stream.Interleaver 112 permutes the bits in the first bit stream generated byencoder 111 on the basis of a first permutation rule. Such permutationis also referred to as interleaving.

Mapper 113 maps the first bit stream permuted by interleaver 112 inaccordance with a first mapping scheme (a first modulation scheme) togenerate a first modulated symbol stream that includes a plurality offirst modulated symbols. In the mapping in accordance with the firstmapping scheme, mapper 113 maps each group of bits that includes a firstnumber of bits in the first bit stream onto one of the signal points ina first constellation, in accordance with the values of such group ofbits.

Encoder 121 encodes an inputted second data series on the basis of asecond error control coding scheme to generate a second bit stream.Interleaver 122 permutes the bits in the second bit stream generated byencoder 121 on the basis of a second permutation rule. Such permutationis also referred to as interleaving.

Mapper 123 maps the second bit stream permuted by interleaver 122 inaccordance with a second mapping scheme (a second modulation scheme) togenerate a second modulated symbol stream that includes a plurality ofsecond modulated symbols. In the mapping in accordance with the secondmapping scheme, mapper 123 maps each group of bits that includes asecond number of bits in the second bit stream onto one of the signalpoints in a second constellation, in accordance with the values of suchgroup of bits.

When a mapping scheme used is PSK modulation such as BPSK and QPSK, orQAM modulation such as 16QAM and 64QAM, each modulated symbol can berepresented by a complex number, for example, with the real partrepresenting the magnitude of the in-phase component and the imaginarypart representing the magnitude of the orthogonal component. Meanwhile,when a mapping scheme used is PAM modulation, each modulated symbol canbe represented by a real number.

Multiplier 114 multiplies each first modulated symbol in the firstmodulated symbol stream by first amplitude coefficient a₁. Multiplier124 multiplies each second modulated symbol in the second modulatedsymbol stream by second amplitude coefficient a₂. Adder 130 superposesfirst modulated symbols multiplied by first amplitude coefficient a₁ andsecond modulated symbols multiplied by second amplitude coefficient a₂to generate a superposed modulated symbol stream that includes aplurality of superposed modulated symbols.

RF unit 140 sends the generated superposed modulated symbol stream as asignal. More specifically, RF unit 140 generates, from the superposedmodulated symbol stream generated by adder 130, a radio-frequency signalas a signal corresponding to the superposed modulated symbol stream tosend such radio-frequency signal from the antenna.

Stated differently, the superposition unit constituted by multiplier114, multiplier 124, and adder 130 superposes the first modulated symbolstream and the second modulated symbol stream at a predeterminedamplitude ratio, thereby generating a multiplexed signal into which thefirst data series and the second data series are multiplexed.Subsequently, RF unit 140 sends the multiplexed signal. Note that themultiplexed signal corresponds to the superposed modulated symbolstream. Also note that the predetermined amplitude ratio may be 1:1, andthat the multiplication may be omitted.

FIG. 2 shows an example configuration of reception device 200 capable ofreceiving and sequentially decoding the signal on which two data seriesare multiplexed onto two layers by superposition coding, and capable ofobtaining (extracting) one of or both of the multiplexed two dataseries. The configuration and operation of reception device 200 will bedescribed with reference to FIG. 2.

Reception device 200 includes RF unit 230, demapper 211, deinterleaver212, decoder 213, encoder 214, interleaver 215, mapper 216, multiplier217, delayer 218, subtractor 219, demapper 221, deinterleaver 222, anddecoder 223. These structural components may also be implemented asdedicated or general-purpose circuits.

Demapper 211, deinterleaver 212, decoder 213, encoder 214, interleaver215, mapper 216, multiplier 217, delayer 218, subtractor 219, demapper221, deinterleaver 222, and decoder 223 can also be representedcollectively as a derivation unit. RF unit 230 can also be representedas a receiver. RF unit 230 may include an antenna.

Reception device 200 receives by an antenna the multiplexed signal sentfrom transmission device 100, and inputs such multiplexed signal into RFunit 230. Stated differently, RF unit 230 receives the multiplexedsignal via the antenna. The multiplexed signal received by RF unit 230is also represented as a received signal, and corresponds to thesuperimposed modulated symbol stream into which the first modulatedsymbol stream and the second modulated symbol stream are multiplexed. RFunit 230 generates a baseband received signal from the radio-frequencyreceived signal.

Demapper 211 demaps the baseband received signal on the basis of thefirst constellation of the first mapping scheme to generate a first bitlikelihood stream. For example, amplitude coefficient a₁ is reflected inthe first constellation for demapping.

Deinterleaver 212 permutes the first bit likelihood stream on the basisof a permutation rule that is a reverse rule of the first permutationrule. Such permutation is also referred to as deinterleaving. Decoder213 performs decoding that is based on the first error control codingscheme by use of the first bit likelihood stream permuted bydeinterleaver 212, and outputs the decoding result as the first dataseries.

Here, of the received signal corresponding to the superposed modulatedsymbol stream, demapper 211 treats the components corresponding to thesecond modulated symbols in the second data series as an unknown signal(noise), and performs demapping on the basis of the first constellationof the first mapping scheme.

When only the first data series is to be obtained, reception device 200terminates the process upon completing the estimation of the first dataseries. Meanwhile, when the second data series is to be obtained inaddition to the first data series, or when only the second data seriesis to be obtained, reception device 200 performs the processes describedbelow to obtain the second data series.

Encoder 214 encodes the first data series obtained by decoder 213 on thebasis of the first error control coding scheme to generate the first bitstream. Interleaver 215 permutes the bits in the first bit streamgenerated by encoder 214 on the basis of the first permutation rule.Such permutation is also referred to as interleaving.

Mapper 216 maps the first bit stream permuted by interleaver 215 inaccordance with the first mapping scheme to generate the first modulatedsymbol stream that includes a plurality of first modulated symbols.Multiplier 217 multiplies the first modulated symbol stream outputted bymapper 216 by first amplitude coefficient a₁.

Delayer 218 delays the received signal outputted from RF unit 230 duringthe time from when RF unit 230 outputs the baseband received signal towhen multiplier 217 outputs the reproduced first modulated symbolstream.

Subtractor 219 subtracts, from the received signal delayed by delayer218, the first modulated symbol stream multiplied by first amplitudecoefficient a₁ by multiplier 217. Through this, subtractor 219 removesthe components corresponding to the first modulated symbols from thereceived signal on which the components corresponding to the firstmodulated symbols and the components and noise corresponding to thesecond modulated symbols are superposed. Subsequently, subtractor 219outputs a signal on which the components and noise corresponding to thesecond modulated symbols are superposed as a signal corresponding to thesecond modulated symbol stream.

Demapper 221 demaps the signal outputted from subtractor 219 on thebasis of the second constellation of the second mapping scheme togenerate a second bit likelihood stream. For example, amplitudecoefficient a₂ is reflected in the second constellation for demapping.

Deinterleaver 222 permutes the second bit likelihood stream on the basisof a permutation rule that is a reverse rule of the second permutationrule. Such permutation is also referred to as deinterleaving. Decoder223 decodes the second bit likelihood stream permuted by deinterleaver222 on the basis of the second error control coding scheme, and outputsthe decoding result as the second data series.

Through the above processes, reception device 200 obtains one of or bothof the first data series and the second data series from the signalreceived by the antenna.

<Superposition Coding>

The following describes superposition coding.

Using signal power P_(s)(W), noise power P_(n)(W), and transmissionbandwidth B (Hz), transmission capacity C_(T) (bit/S) is given as theShannon limit by Equation 1.

$\begin{matrix}\left\lbrack {{Math}.\mspace{14mu} 1} \right\rbrack & \; \\{C_{T} = {B \cdot {\log_{2}\left( {1 + \frac{P_{s}}{P_{n}}} \right)}}} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$

Transmission capacity C (bit/s/Hz) per Hz normalized by the transmissionbandwidth is given by Equation 2.

$\begin{matrix}\left\lbrack {{Math}.\mspace{14mu} 2} \right\rbrack & \; \\{C = {\log_{2}\left( {1 + \frac{P_{s}}{P_{n}}} \right)}} & \left( {{Equation}\mspace{14mu} 2} \right)\end{matrix}$

In the following, “transmission capacity per Hz” will be simply referredto as “transmission capacity.”

In superposition coding of the first data series and the second dataseries, signal power P_(s1)(W) of the first layer corresponding to thefirst data series, signal power P_(s2)(W) of the second layercorresponding to the second data series, and the entire signal powerP_(s)(W) satisfy: P_(s)=P_(s1)+P_(s2).

When demodulating the first layer, reception device 200 regards thecomponents of the modulated symbols in the second layer as unknowncomponents superposed on the modulated symbols in the first layer, i.e.,noise. As such, transmission capacity C₁ of the first layer is given byEquation 3.

$\begin{matrix}\left\lbrack {{Math}.\mspace{14mu} 3} \right\rbrack & \; \\{C_{1} = {\log_{2}\left( {1 + \frac{P_{s\; 1}}{P_{s\; 2} + P_{n}}} \right)}} & \left( {{Equation}\mspace{14mu} 3} \right)\end{matrix}$

When reception device 200 demodulates the second layer, the componentsof the modulated symbols in the first layer have already been removedfrom the received signal. As such, transmission capacity C₂ of thesecond layer is given by Equation 4.

$\begin{matrix}\left\lbrack {{Math}.\mspace{14mu} 4} \right\rbrack & \; \\{C_{2} = {\log_{2}\left( {1 + \frac{P_{s\; 2}}{P_{n}}} \right)}} & \left( {{Equation}\mspace{14mu} 4} \right)\end{matrix}$

As shown by Equation 5, the total of transmission capacity C₁ of thefirst layer and transmission capacity C₂ of the second layer agrees withthe Shannon limit.

$\begin{matrix}\left\lbrack {{Math}.\mspace{14mu} 5} \right\rbrack & \; \\\begin{matrix}{{C_{1} + C_{2}} = {{\log_{2}\left( {1 + \frac{P_{s\; 1}}{P_{s\; 2} + P_{n}}} \right)} + {\log_{2}\left( {1 + \frac{P_{s\; 2}}{P_{n}}} \right)}}} \\{= {{\log_{2}\left( \frac{P_{s} + P_{n}}{P_{s\; 2} + P_{n}} \right)} + {\log_{2}\left( \frac{P_{s\; 2} + P_{n}}{P_{n}} \right)}}} \\{= {\log_{2}\left( \frac{P_{s} + P_{n}}{P_{n}} \right)}} \\{= {\log_{2}\left( {1 + \frac{P_{s}}{P_{n}}} \right)}}\end{matrix} & \left( {{Equation}\mspace{14mu} 5} \right)\end{matrix}$

In the present embodiment, signal power P_(s1) of the first layercorresponding to the first data series is proportional to the secondpower of first amplitude coefficient a₁, and signal power P_(s2) of thesecond layer corresponding to the second data series is proportional tothe second power of second amplitude coefficient a₂. The allocation ofsignal power to a plurality of layers is determined by an amplitudecoefficient that is multiplied to the modulated symbols of each layer.

FIG. 3 shows an example simulation result of each transmission capacitywhen the ratio between signal power P_(s1) of the first layer and signalpower P_(s2) of the second layer is P_(s1):P_(s2)=2:1. In FIG. 3, thelateral axis represents as dB (decibel) the ratio of signal power P_(s)to noise power P_(n) (SNR), and the vertical axis representstransmission capacity. In FIG. 3, the dot-and-dash line indicatestransmission capacity C₁ of the first layer, the broken line indicatestransmission capacity C₂ of the second layer, and the solid lineindicates the total transmission capacity of transmission capacity C₁ ofthe first layer and transmission capacity C₂ of the second layer.

Note that SNR, which means a ratio of signal power to noise power, isalso referred to as a signal-to-noise power ratio or a signal-to-noiseratio.

<Non-Uniform Constellation>

Transmission device 100 according to the present embodiment can employany mapping scheme for each of the first mapping scheme and the secondmapping scheme. Reception device 200 demodulates the first layer, withthe second modulated symbols of the second layer remaining unknown. Assuch, a mapping scheme such as QPSK, for example, that mainly supports alow SNR is suitable as the first mapping scheme.

FIG. 4 shows an example QPSK constellation. More specifically, four QPSKsignal points are plotted in the complex plane, with the lateral axisrepresenting the real part (the real component) and the vertical axisrepresenting the imaginary part (the imaginary component). In QPSK, agroup of bits (00, 01, 10, or 11) is associated with a modulated symbolindicating a complex number on the basis of the constellation shown inFIG. 4. Meanwhile, the second layer is demodulated with the modulatedsymbols in the first layer having been removed. As such, the secondmapping scheme may be a mapping scheme that utilizes multilevelconstellation supporting a high SNR.

Non-uniform constellations as disclosed in “J. Zoellner and N. Loghin,Optimization of High-order Non-uniform QAM Constellations, IEEEInternational Symposium on Broadband Multimedia Systems and Broadcasting2013” have received recent attention as multilevel constellations.Unlike conventional uniform constellations that include uniformly spacedsignal points, such as a QAM constellation, a non-uniform constellationincludes ununiformly spaced signal points. In some cases, a mappingscheme using a non-uniform constellation improves the transmissioncapacity compared to a mapping scheme using a uniform constellation.

FIG. 5 shows an example non-uniform constellation including 256 signalpoints (Nu-256QAM). In FIG. 5, 256 non-uniform constellation signalpoints are plotted in the complex plane, with the lateral axisrepresenting the real part and the vertical axis representing theimaginary part.

The following describes an example of using QPSK shown in FIG. 4 as thefirst mapping scheme and Nu-256QAM shown in FIG. 5 as the second mappingscheme in the multiplexing scheme that utilizes superposition coding.

FIG. 6 shows an example simulation result of each transmission capacitywhen the ratio between signal power P_(s1) of the first layer and signalpower P_(s2) of the second layer is P_(s1):P_(s2)=2:1. In FIG. 6, thelateral axis represents as dB (decibel) the ratio of signal power P_(s)to noise power Pi, (SNR), and the vertical axis represents transmissioncapacity. In FIG. 6, the dot-and-dash line indicates transmissioncapacity C₁ of the first layer, and the broken line indicatestransmission capacity C₂ of the second layer. A combination of QPSK andNu-256QAM achieves a transmission capacity that is close to the limitshown in FIG. 3.

As described above, transmission device 100 according to the presentembodiment is capable of highly efficient multiplexing and transmissionof a plurality of data series by a multiplexing scheme utilizingsuperposition coding. Reception device 200 is capable of receiving aplurality of data series that have been multiplexed in a highlyefficient manner by the multiplexing scheme utilizing superpositioncoding. Transmission device 100 and reception device 200 are alsocapable of increasing the transmission capacity by use of a non-uniformconstellation.

Note that permutation (interleaving and deinterleaving) reduces theeffects that may be caused when successive errors occur. Permutation(interleaving and deinterleaving) also controls the correspondence amongbits included in codewords in error correcting coding, modulatedsymbols, and bits included in such modulated symbols. However, suchpermutation (interleaving and deinterleaving) may be omitted.

Stated differently, interleaver 112 and interleaver 122 are optionalstructural components, and thus may not be included in transmissiondevice 100. Similarly, deinterleaver 212, interleaver 215, anddeinterleaver 222 are optional structural components, and thus may notbe included in reception device 200.

Interleaving and deinterleaving, however, make a pair. As such, whentransmission device 100 includes interleaver 112 and interleaver 122,reception device 200 basically includes deinterleaver 212, interleaver215, and deinterleaver 222. Meanwhile, when transmission device 100 doesnot include interleaver 112 and interleaver 122, reception device 200does not include deinterleaver 212, interleaver 215, and deinterleaver222.

Also, amplitude coefficient a₁ may be reflected in the mapping performedby mapper 216 of reception device 200. In such a case, reception device200 may omit the multiplication, and thus may not include multiplier217.

Error control coding on the first data series and the second data seriesmay be performed by an external device that is different fromtransmission device 100. In such a case, transmission device 100 mayomit the error control coding, and may not include encoder 111 andencoder 121.

Embodiment 2

<Parallel Decoding of Signal Obtained by Superposition Coding>

The present embodiment describes a reception method for paralleldecoding of a signal obtained by superposition coding. The configurationof the transmission device is the same as the configuration oftransmission device 100 shown in FIG. 1, and thus will not be described.In parallel decoding in superposition coding, the reception devicetreats the components of the modulated symbol stream in the first layeras an unknown signal (noise) to decode the second layer, withoutremoving the components of the modulated symbol stream in the firstlayer included in the received signal.

FIG. 7 shows an example configuration of reception device 300 capable ofreceiving and performing parallel decoding on the signal on which twodata series are multiplexed onto two layers by superposition coding, andcapable of obtaining one of or both of the multiplexed two data series.The configuration and operation of reception device 300 will bedescribed with reference to FIG. 7.

Reception device 300 includes RF unit 330, demapper 310, deinterleaver312, decoder 313, deinterleaver 322, and decoder 323. These structuralcomponents may also be implemented as dedicated or general-purposecircuits. Demapper 310, deinterleaver 312, decoder 313, deinterleaver322, and decoder 323 can also be represented collectively as aderivation unit. RF unit 330 can also be represented as a receiver. RFunit 330 may include an antenna.

Reception device 300 receives by an antenna the multiplexed signal sentfrom transmission device 100, and inputs such multiplexed signal into RFunit 330. Stated differently, RF unit 330 receives the multiplexedsignal via the antenna. The multiplexed signal received by RF unit 330is also represented as a received signal. RF unit 330 generates abaseband received signal from the radio-frequency received signal.

Demapper 310 demaps the baseband received signal to generate the firstbit likelihood stream and the second bit likelihood stream. For example,demapper 310 performs such demapping on the basis of a superpositionconstellation that shows the arrangement of the signal points ofsuperposed modulated symbols obtained by superposing the first modulatedsymbols and the second modulated symbols by superposition coding.

The superposition constellation is determined in accordance with thefirst constellation of the first mapping scheme, the secondconstellation of the second mapping scheme, first amplitude coefficienta₁, second amplitude coefficient a₂, etc.

FIG. 8 shows an example superposition constellation, which is morespecifically a combination of the QPSK constellation shown in FIG. 4 andthe Nu-256QAM constellation shown in FIG. 5. Even more specifically, theNu-256QAM constellation (256 signal points) is placed on each of thefour regions in the complex plane in accordance with the four signalpoints of the QPSK constellation. These four regions, each correspondingto Nu-256QAM constellation, may partially overlap with each other.

Demapper 310 performs demapping on the basis of the superpositionconstellation as shown in FIG. 8. Stated differently, demapper 310generates the first bit likelihood stream, with the modulated symbolstream of the second layer remaining unknown, and generates the secondbit likelihood stream, with the modulated symbol stream of the firstlayer remaining unknown.

Note that demapper 310 may use the first constellation of the firstmapping scheme to generate the first bit likelihood stream, and may usethe above-described superposition constellation to generate the secondbit likelihood stream.

The first constellation, when used to generate the first bit likelihoodstream, enables demapper 310 to reduce the number of signal points thatshould be considered in generating the first bit likelihood stream,compared to when the superposition constellation is also used togenerate the first bit likelihood stream. This thus enables demapper 310to reduce the number of arithmetic computations.

Demapper 310 corresponds, for example, to the first demapper that demapsthe received signal to generate the first bit likelihood stream and thesecond demapper that demaps the received signal to generate the secondbit likelihood stream. Demapper 310 may include the first demapper thatdemaps the received signal to generate the first bit likelihood streamand the second demapper that demaps the received signal to generate thesecond bit likelihood stream.

Deinterleaver 312 permutes the first bit likelihood stream on the basisof a permutation rule that is a reverse rule of the first permutationrule. Such permutation is also referred to as deinterleaving. Decoder313 decodes the first bit likelihood stream permuted by deinterleaver312 on the basis of the first error control coding scheme, and outputsthe decoding result as the first data series.

Deinterleaver 322 permutes the second bit likelihood stream on the basisof a permutation rule that is a reverse rule of the second permutationrule. Such permutation is also referred to as deinterleaving. Decoder323 decodes the second bit likelihood stream permuted by deinterleaver322 on the basis of the second error control coding scheme, and outputsthe decoding result as the second data series.

Note that permutation (deinterleaving) may be omitted as in the case ofEmbodiment 1. Stated differently, deinterleaver 312 and deinterleaver322 are optional structural components, and thus may not be included inreception device 300.

Interleaving and deinterleaving, however, make a pair. As such, whentransmission device 100 includes interleaver 112 and interleaver 122,reception device 300 basically includes deinterleaver 312 anddeinterleaver 322. Meanwhile, when transmission device 100 does notinclude interleaver 112 and interleaver 122, reception device 300 doesnot include deinterleaver 312 and deinterleaver 322.

FIG. 9 is a flowchart of example operations performed by receptiondevice 300. First, RF unit 330 receives the multiplexed signal intowhich the first data series and the second data series are multiplexed(S101).

Next, demapper 310 demaps the multiplexed signal to generate the firstbit likelihood stream of the first data series (S102). Demapper 310demaps the multiplexed signal to generate the second bit likelihoodstream of the second data series (S103). Deinterleaver 312 maydeinterleave such generated first bit likelihood stream. Also,deinterleaver 322 may deinterleave such generated second bit likelihoodstream.

Then, decoder 313 performs error control decoding on the first bitlikelihood stream to derive the first data series (S104). Also, decoder323 performs error control decoding on the second bit likelihood streamto derive the second data series (S105).

Note that processes on the first bit likelihood stream (generation,deinterleaving, and error control decoding) and processes on the secondbit likelihood stream (generation, deinterleaving, and error controldecoding) are basically performed in parallel.

Reception device 300 as shown in FIG. 7 that performs parallel decodinghas lower performance in decoding the second layer than that ofreception device 200 as shown in FIG. 2 that performs sequentialdecoding.

FIG. 10 shows an example simulation result of the transmission capacityof the second layer when the ratio between signal power P_(s1) of thefirst layer and signal power P_(s2) of the second layer isP_(s1):P_(s2)=2:1. In FIG. 10, the lateral axis represents as dB(decibel) the ratio of signal power P_(s) to noise power Pn (SNR), andthe vertical axis represents transmission capacity. In FIG. 10, thesolid line indicates the transmission capacity of the second layer whensequential decoding is performed, and the broken line indicates thetransmission capacity of the second layer when parallel decoding isperformed.

As FIG. 10 shows, in the decoding of the second layer, parallel decodinginvolves an increased SNR with respect to the same transmission capacityand a decreased transmission capacity with respect to the same SNR,compared to sequential decoding.

As described above, reception device 300 according to the presentembodiment that performs parallel decoding has lower performance indecoding the second data series transmitted on the second layer thanthat of reception device 200 that performs sequential decoding. However,reception device 300 reduces the number of structural componentsrequired for decoding the second layer.

More specifically, reception device 300 eliminates the need for encoder214, interleaver 215, mapper 216, and multiplier 217 that are requiredby reception device 200 shown in FIG. 2 performing sequential decodingto reproduce the modulated symbol stream of the first layer. Receptiondevice 300 also eliminates the need for delayer 218 that delays thereceived signal and subtractor 219 that removes the components of themodulated symbols in the first layer reproduced from the receivedsignal.

The circuit size can be thus reduced. Reception device 300 also requiresa smaller number of arithmetic computations and lower power consumptionthan are required by reception device 200.

Reception device 200 shown in FIG. 2 that performs sequential decodingdemodulates the first layer in the received signal to obtain the firstdata series, generates the first modulated symbol stream from theobtained first data series, and then starts demodulating the secondlayer in the received signal to obtain the second data series.Meanwhile, reception device 300 according to the present embodiment thatperforms parallel decoding is capable of simultaneously obtaining thefirst data series and the second data series in parallel, therebyreducing processing delays.

Alternatively, the reception device may observe the SNR of the receivedsignal to make selection between parallel decoding to be performed whenthe SNR is high and sequential decoding to be performed when the SNR islow.

In such a case, reception device 200 shown in FIG. 2 includes, forexample, a controller that makes selection between sequential decodingand parallel decoding depending on the SNR. Such controller may beincluded in RF unit 230 or demapper 221. Furthermore, demapper 221 isconfigured to perform demapping based on the superpositionconstellation, which is described as an operation performed by demapper310 shown in FIG. 7, in addition to demapping that is based on thesecond constellation.

Demapper 221 switches between demapping to be performed on the signaloutputted from subtractor 219 on the basis of the second constellationand demapping to be performed on the signal outputted from RF unit 230on the basis of the superposition constellation. For example, demapper221 switches between these demapping operations in accordance with acontrol signal from the controller.

FIG. 11 shows an example configuration of reception device 400 thatselectively performs parallel decoding and sequential decoding.Reception device 400 includes RF unit 430, demapper 411, deinterleaver412, decoder 413, encoder 414, interleaver 415, mapper 416, multiplier417, delayer 418, subtractor 419, demapper 421, deinterleaver 422, anddecoder 423. Structural components of reception device 400 shown in FIG.11 and structural components of reception device 200 shown in FIG. 2 arebasically the same.

However, demapper 421 of reception device 400 performs demapping that isbased on the superposition constellation in addition to demapping thatis based on the second constellation of the second mapping scheme. Forexample, depending on the SNR, demapper 421 switches between demappingto be performed on the signal outputted from subtractor 419 on the basisof the second constellation and demapping to be performed on the signaloutputted from RF unit 430 on the basis of the superpositionconstellation.

Although the example shown in FIG. 11 omits a controller that makesselection between sequential decoding and parallel decoding depending onthe SNR, the controller may be included in demapper 421, in RF unit 430,or in reception device 400 as a new structural component.

FIG. 12 is a flowchart of example operations performed by receptiondevice 400. First, RF unit 430 receives the multiplexed signal intowhich the first data series and the second data series are multiplexed(S201). Then, RF unit 430 determines whether the multiplexed signalsatisfies a predetermined requirement. The predetermined requirement,for example, is that the SNR should be higher than a predeterminedthreshold.

When the multiplexed signal satisfies the predetermined requirement (Yesin S202), demapper 411 demaps the multiplexed signal to generate thefirst bit likelihood stream of the first data series (S203). Also,demapper 421 demaps the multiplexed signal to generate the second bitlikelihood stream of the second data series (S204). Deinterleaver 412may deinterleave such generated first bit likelihood stream. Also,deinterleaver 422 may deinterleave such generated second bit likelihoodstream.

Decoder 413 performs error control decoding on the first bit likelihoodstream to derive the first data series (S205). Also, decoder 423performs error control decoding on the second bit likelihood stream toderive the second data series (S206).

These operations (S203 to S206) are basically the same as the operations(S102 to S105) shown in FIG. 9.

Meanwhile, when the multiplexed signal fails to satisfy thepredetermined requirement (No in S202), demapper 411 demaps themultiplexed signal to generate the first bit likelihood stream of thefirst data series (S207). Deinterleaver 412 may deinterleave suchgenerated first bit likelihood stream. Then, decoder 413 performs errorcontrol decoding on the first bit likelihood stream to derive the firstdata series (S208).

Next, encoder 414 performs error control coding on the first data seriesto generate the first bit stream (S209). Interleaver 415 may interleavesuch generated first bit stream. Then, mapper 416 maps the first bitstream to generate the first modulated symbol stream (S210). Multiplier417 may multiply the first modulated symbol stream by amplitudecoefficient a₁.

Delayer 418 delays the multiplexed signal until the first modulatedsymbol stream is generated (S211). Then, subtractor 419 subtracts thefirst modulated symbol stream from the multiplexed signal (S212).

Next, demapper 421 demaps the multiplexed signal from which the firstmodulated symbol stream has been subtracted to generate the second bitlikelihood stream (S213). Deinterleaver 422 may deinterleave suchgenerated second bit likelihood stream. Then, decoder 423 performs errorcontrol decoding on the second bit likelihood stream to derive thesecond data series (S214).

Through these operations, reception device 400 performs paralleldecoding when the SNR is high, thereby reducing the number of arithmeticcomputations and power consumption. Reception device 400 also performsparallel decoding when the SNR is high, thereby reducing processingdelays. Meanwhile, reception device 400 performs sequential decodingwhen the SNR is low, thereby increasing the possibility of correctlydecoding the second data series.

Note that the first mapping scheme and the second mapping schemeaccording to the present embodiment are basically the same as the firstmapping scheme and the second mapping scheme according to Embodiment 1.Stated differently, the first constellation and the second constellationaccording to the present embodiment are basically the same as the firstconstellation and the second constellation according to Embodiment 1.Any one of a uniform constellation and a non-uniform constellation maybe used as the second mapping scheme.

Embodiment 3

<Variation of Superposition Coding (Modified Superposition Coding)>

The present embodiment describes a method of multiplexing andtransmitting a plurality of data series by a variation of superpositioncoding (modified superposition coding), which is a modified version ofthe above-described superposition coding.

FIG. 13 shows an example configuration of transmission device 500 thatmultiplexes two data series onto two layers by the variation ofsuperposition coding, and transmits a multiplexed data series. Theconfiguration and operation of transmission device 500 will be describedwith reference to FIG. 13.

Transmission device 500 includes encoder 511, interleaver 512, mapper513, multiplier 514, encoder 521, interleaver 522, mapper 523, converter525, multiplier 524, adder 530, and RF unit 540. These structuralcomponents may also be implemented as dedicated or general-purposecircuits. Multiplier 514, multiplier 524, and adder 530 can also berepresented collectively as a superposition unit. RF unit 540 can alsobe represented as a transmitter. RF unit 540 may include an antenna.

Encoder 511 encodes an inputted first data series on the basis of afirst error control coding scheme to generate a first bit stream.Interleaver 512 permutes the bits in the first bit stream generated byencoder 511 on the basis of a first permutation rule. Such permutationis also referred to as interleaving.

Mapper 513 maps the first bit stream permuted by interleaver 512 inaccordance with a first mapping scheme to generate a first modulatedsymbol stream that includes a plurality of first modulated symbols. Inthe mapping in accordance with the first mapping scheme, mapper 513 mapseach group of bits that includes a first number of bits in the first bitstream onto one of the signal points in a first constellation inaccordance with the values of such group of bits.

When PSK modulation such as BPSK and QPSK, or QAM modulation such as16QAM and 64QAM is used as the first mapping scheme, each firstmodulated symbol can be represented by a complex number, for example,with the real part representing the magnitude of the in-phase componentand the imaginary part representing the magnitude of the orthogonalcomponent. Meanwhile, when PAM modulation is used as the first mappingscheme, each first modulated symbol can be represented by a real number.

Encoder 521 encodes an inputted second data series on the basis of asecond error control coding scheme to generate a second bit stream.Interleaver 522 permutes the bits in the second bit stream generated byencoder 521 on the basis of a second permutation rule. Such permutationis also referred to as interleaving.

Mapper 523 maps the second bit stream permuted by interleaver 522 inaccordance with a second mapping scheme to generate a second modulatedsymbol stream that includes a plurality of second modulated symbols. Inthe mapping in accordance with the second mapping scheme, mapper 523maps each group of bits that includes a second number of bits in thesecond bit stream onto one of the signal points in a secondconstellation in accordance with the values of such group of bits.

When PSK modulation such as BPSK and QPSK, or QAM modulation such as16QAM and 64QAM is used as the second mapping scheme, each secondmodulated symbol can be represented by a complex number, for example,with the real part representing the magnitude of the in-phase componentand the imaginary part representing the magnitude of the orthogonalcomponent. Meanwhile, when PAM modulation is used as the second mappingscheme, each second modulated symbol can be represented by a realnumber. Any one of a uniform constellation and a non-uniformconstellation may be used as the second mapping scheme.

Converter 525 converts each second modulated symbol to be superposedwith the corresponding first modulated symbol, on the basis of thevalues of the bits used to generate such first modulated symbol. Throughthis, converter 525 converts the second modulated symbol stream.

Multiplier 514 multiplies each first modulated symbol in the firstmodulated symbol stream by first amplitude coefficient a₁. Multiplier524 multiplies, by second amplitude coefficient a₂, each secondmodulated symbol in the second modulated symbol stream converted byconverter 525. Adder 530 superposes first modulated symbols multipliedby first amplitude coefficient a₁ and second modulated symbolsmultiplied by second amplitude coefficient a₂ to generate a superposedmodulated symbol stream that includes a plurality of superposedmodulated symbols.

RF unit 540 sends the generated superposed modulated symbol stream as asignal. More specifically, RF unit 540 generates, from the superposedmodulated symbol stream generated by adder 530, a radio-frequency signalas a signal corresponding to the superposed modulated symbol stream tosend such radio-frequency signal from the antenna.

Stated differently, the superposition unit constituted by multiplier514, multiplier 524, and adder 530 superposes the first modulated symbolstream and the second modulated symbol stream at a predeterminedamplitude ratio, thereby generating a multiplexed signal into which thefirst data series and the second data series are multiplexed.Subsequently, RF unit 540 sends the multiplexed signal. Note that themultiplexed signal corresponds to the superposed modulated symbolstream. Also note that the predetermined amplitude ratio may be 1:1, andthat the multiplication may be omitted. The following shows an examplecase in which QPSK is used as the first mapping scheme to describe theoperation of converter 525.

For example, when S₁(t) is the t-th modulated symbol in the firstmodulated symbol stream generated by mapper 513, and b₁(t) and b₂(t) area plurality of bits to be mapped onto S₁(t), modulated symbol S₁(t) isgiven by Equation 6.

$\begin{matrix}\left\lbrack {{Math}.\mspace{14mu} 6} \right\rbrack & \; \\{{S_{1}(t)} = \frac{\left( {{2 \cdot {b_{1}(t)}} - 1} \right) + {i \cdot \left( {{2 \cdot {b_{2}(t)}} - 1} \right)}}{\sqrt{2}}} & \left( {{Equation}\mspace{14mu} 6} \right)\end{matrix}$

Here, i denotes the imaginary unit. Modulated symbol S₁(t) may also begiven by an equation in which the polarity (positive/negative) of one ofor both of the real part and the imaginary part of Equation 6 arereversed. Bit b₁(t) is a bit that contributes to the real part ofmodulated symbol S₁(t). Bit b₂(t) is a bit that contributes to theimaginary part of modulated symbol S₁(t).

Converter 525 converts, into, S′₂(t), the t-th modulated symbol S₂(t) inthe second modulated symbol stream generated by mapper 523, on the basisof b₁(t) and b₂(t) as shown by Equation 7.

[Math. 7]

S′ ₂(t)=(−1)^(b) ¹ ^((t)) ·Re[S ₂(t)]+i·(−1)^(b) ² ^((t)) ·Im[S₂(t)]  (Equation 7)

Here, S′₂(t) is the converted t-th modulated symbol in the secondmodulated symbol stream. Re[S₂(t)] is the value of the real part ofS₂(t), and Im[S₂(t)] is the value of the imaginary part of S₂(t).Modulated symbol S′₂(t) may be given by an equation in which thepolarity of one of or both of the real part and the imaginary part ofEquation 7 are reversed.

As described above, the variation of superposition coding controls thepolarities of the real part and the imaginary part of each secondmodulated symbol in accordance with the values of the bits to be mappedonto the first modulated symbol that is superposed with such secondmodulated symbol. Note that the polarities of the real part and theimaginary part of each second modulated symbol may be controlled inaccordance with the first modulated symbol that is superposed with suchsecond modulated symbol. Also, the polarity of one of the real part andthe imaginary part of each second modulated symbol may be controlled, orthe polarities of both the real part and the imaginary part of eachsecond modulated symbol may be controlled.

FIG. 14 shows an example configuration of transmission device 600 thatmultiplexes two data series onto two layers by the variation ofsuperposition coding, and transmits the multiplexed data series. Theconfiguration of transmission device 600 is different from theconfiguration of transmission device 500. The configuration andoperation of transmission device 600 will be described with reference toFIG. 14.

Transmission device 600 includes encoder 611, interleaver 612, mapper613, multiplier 614, encoder 621, interleaver 622, mapper 623, converter625, multiplier 624, adder 630, and RF unit 640. These structuralcomponents may also be implemented as dedicated or general-purposecircuits. Multiplier 614, multiplier 624, and adder 630 can also berepresented collectively as a superposition unit. RF unit 640 can alsobe represented as a transmitter. RF unit 640 may include an antenna.

Encoder 611 encodes an inputted first data series on the basis of afirst error control coding scheme to generate a first bit stream.Interleaver 612 permutes the bits in the first bit stream generated byencoder 611 on the basis of a first permutation rule. Such permutationis also referred to as interleaving.

Mapper 613 maps the first bit stream permuted by interleaver 612 inaccordance with a first mapping scheme to generate a first modulatedsymbol stream that includes a plurality of first modulated symbols. Inthe mapping in accordance with the first mapping scheme, mapper 613 mapseach group of bits that includes a first number of bits in the first bitstream onto one of the signal points in a first constellation inaccordance with the values of such group of bits.

Encoder 621 encodes an inputted second data series on the basis of asecond error control coding scheme to generate a second bit stream.Interleaver 622 permutes the bits in the second bit stream generated byencoder 621 on the basis of a second permutation rule. Such permutationis also referred to as interleaving.

Mapper 623 maps the second bit stream permuted by interleaver 622 inaccordance with a second mapping scheme to generate a second modulatedsymbol stream that includes a plurality of second modulated symbols. Inthe mapping in accordance with the second mapping scheme, mapper 623maps each group of bits that includes a second number of bits in thesecond bit stream onto one of the signal points in a secondconstellation in accordance with the values of such group of bits.

Converter 625 converts each second modulated symbol to be superposedwith the corresponding first modulated symbol, on the basis of thegenerated first modulated symbol. Through this, converter 625 convertsthe second modulated symbol stream.

Multiplier 614 multiplies each first modulated symbol in the firstmodulated symbol stream by first amplitude coefficient a₁. Multiplier624 multiplies, by second amplitude coefficient a₂, each secondmodulated symbol in the second modulated symbol stream converted byconverter 625. Adder 630 superposes first modulated symbols multipliedby first amplitude coefficient a₁ and second modulated symbolsmultiplied by second amplitude coefficient a₂ to generate a superposedmodulated symbol stream that includes a plurality of superposedmodulated symbols.

RF unit 640 sends the generated superposed modulated symbol stream as asignal. More specifically, RF unit 640 generates, from the superposedmodulated symbol stream generated by adder 630, a radio-frequency signalas a signal corresponding to the superposed modulated symbol stream tosend such radio-frequency signal from the antenna.

Stated differently, the superposition unit constituted by multiplier614, multiplier 624, and adder 630 superposes the first modulated symbolstream and the second modulated symbol stream at a predeterminedamplitude ratio, thereby generating a multiplexed signal into which thefirst data series and the second data series are multiplexed.Subsequently, RF unit 640 sends the multiplexed signal. Note that themultiplexed signal corresponds to the superposed modulated symbolstream. Also note that the predetermined amplitude ratio may be 1:1, andthat the multiplication may be omitted.

The following shows an example case in which QPSK is used as the firstmapping scheme to describe the operation of converter 625.

For example, when S₁(t) is the t-th modulated symbol in the firstmodulated symbol stream generated by mapper 613, and b₁(t) and b₂(t) area plurality of bits to be mapped onto S₁(t), modulated symbol S₁(t) isgiven by Equation 8.

$\begin{matrix}\left\lbrack {{Math}.\mspace{14mu} 8} \right\rbrack & \; \\{{S_{1}(t)} = \frac{\left( {{2 \cdot {b_{1}(t)}} - 1} \right) + {i \cdot \left( {{2 \cdot {b_{2}(t)}} - 1} \right)}}{\sqrt{2}}} & \left( {{Equation}\mspace{14mu} 8} \right)\end{matrix}$

Here, i denotes the imaginary unit. Modulated symbol S₁(t) may also begiven by an equation in which the polarity of one of or both of the realpart and the imaginary part of Equation 8 are reversed. Bit b₁(t) is abit that contributes to the real part of modulated symbol S₁(t). Bitb₂(t) is a bit that contributes to the imaginary part of modulatedsymbol S₁(t).

Converter 625 converts, into S′₂(t), the t-th modulated symbol S₂(t) inthe second modulated symbol stream generated by mapper 623, on the basisof modulated symbol S₁(t) as shown by Equation 9.

[Math. 9]

S′ ₂(t)=−sgn(Re[S ₁(t)])·Re[S ₂(t)]−i·sgn(Im[S ₁(t)])·Im[S ₂(t)]  (Equation 9)

Here, S′₂(t) is the converted t-th modulated symbol in the secondmodulated symbol stream. Re[S₂(t)] is the value of the real part ofS₂(t), and Im[S₂(t)] is the value of the imaginary part of S₂(t). Also,sgn(Re[S₁(t)] is the polarity of the real part of S₁(t), andsgn(Im[S₁(t)] is the polarity of the imaginary part of S₁(t).

Modulated symbol S′₂(t) may be given by an equation in which thepolarity of one of or both of the real part and the imaginary part ofEquation 9 are reversed. Note that the conversion that is based onEquation 9 is substantially the same as the conversion that is based onEquation 7.

As described above, the variation of superposition coding controls thepolarities of the real part and the imaginary part of each secondmodulated symbol in accordance with the first modulated symbol that issuperposed with such second modulated symbol. Note that the polaritiesof the real part and the imaginary part of each second modulated symbolmay be controlled in accordance with the values of the bits to be mappedonto the first modulated symbol that is superposed with such secondmodulated symbol. Also, the polarity of one of the real part and theimaginary part of each second modulated symbol may be controlled, or thepolarities of both the real part and the imaginary part of each secondmodulated symbol may be controlled.

FIG. 15 shows an example configuration of transmission device 700 thatmultiplexes two data series onto two layers by the variation ofsuperposition coding, and transmits the multiplexed data series. Theconfiguration of transmission device 700 is different from theconfigurations of transmission devices 500 and 600. The configurationand operation of transmission device 700 will be described withreference to FIG. 15.

Transmission device 700 includes encoder 711, interleaver 712, mapper713, multiplier 714, encoder 721, interleaver 722, mapper 723,multiplier 724, adder 730, and RF unit 740. These structural componentsmay also be implemented as dedicated or general-purpose circuits.Multiplier 714, multiplier 724, and adder 730 can also be representedcollectively as a superposition unit. RF unit 740 can also berepresented as a transmitter. RF unit 740 may include an antenna. Mapper723 may include a converter.

Encoder 711 encodes an inputted first data series on the basis of afirst error control coding scheme to generate a first bit stream.Interleaver 712 permutes the bits in the first bit stream generated byencoder 711 on the basis of a first permutation rule. Such permutationis also referred to as interleaving.

Mapper 713 maps the first bit stream permuted by interleaver 712 inaccordance with a first mapping scheme to generate a first modulatedsymbol stream that includes a plurality of first modulated symbols. Inthe mapping in accordance with the first mapping scheme, mapper 713 mapseach group of bits that includes a first number of bits in the first bitstream onto one of the signal points in a first constellation inaccordance with the values of such group of bits.

Encoder 721 encodes an inputted second data series on the basis of asecond error control coding scheme to generate a second bit stream.Interleaver 722 permutes the bits in the second bit stream generated byencoder 721 on the basis of a second permutation rule. Such permutationis also referred to as interleaving.

Mapper 723 converts (modifies) a second mapping scheme in accordancewith the first bit stream to be mapped to the first modulated symbolstream by mapper 713. Mapper 723 then maps the second bit streaminterleaved by interleaver 722 in accordance with the second mappingscheme that has been converted in accordance with the first bit stream.Through these processes, mapper 723 generates a second modulated symbolstream that includes a plurality of second modulated symbols.

In the mapping in accordance with the second mapping scheme, mapper 723maps each group of bits that includes a second number of bits in thesecond bit stream onto one of the signal points in a secondconstellation in accordance with the values of such group of bits.

Multiplier 714 multiplies each first modulated symbol in the firstmodulated symbol stream by first amplitude coefficient a₁. Multiplier724 multiplies each second modulated symbol in the second modulatedsymbol stream by second amplitude coefficient a₂. Adder 730 superposesfirst modulated symbols multiplied by first amplitude coefficient a₁ andsecond modulated symbols multiplied by second amplitude coefficient a₂to generate a superposed modulated symbol stream that includes aplurality of superposed modulated symbols.

RF unit 740 sends the generated superposed modulated symbol stream as asignal. More specifically, RF unit 740 generates, from the superposedmodulated symbol stream generated by adder 730, a radio-frequency signalas a signal corresponding to the superposed modulated symbol stream tosend such radio-frequency signal from the antenna.

Stated differently, the superposition unit constituted by multiplier714, multiplier 724, and adder 730 superposes the first modulated symbolstream and the second modulated symbol stream at a predeterminedamplitude ratio, thereby generating a multiplexed signal into which thefirst data series and the second data series are multiplexed.Subsequently, RF unit 740 sends the multiplexed signal. Note that themultiplexed signal corresponds to the superposed modulated symbolstream. Also note that the predetermined amplitude ratio may be 1:1, andthat the multiplication may be omitted.

The following shows an example case in which QPSK is used as the firstmapping scheme to describe the operation of mapper 723.

For example, when S₁(t) is the t-th modulated symbol in the firstmodulated symbol stream generated by mapper 713, and b₁(t) and b₂(t) area plurality of bits to be mapped onto S₁(t), modulated symbol S₁(t) isgiven by Equation 10.

$\begin{matrix}\left\lbrack {{Math}.\mspace{14mu} 10} \right\rbrack & \; \\{{S_{1}(t)} = \frac{\left( {{2 \cdot {b_{1}(t)}} - 1} \right) + {i \cdot \left( {{2 \cdot {b_{2}(t)}} - 1} \right)}}{\sqrt{2}}} & \left( {{Equation}\mspace{14mu} 10} \right)\end{matrix}$

Here, i denotes the imaginary unit. Modulated symbol S₁(t) may also begiven by an equation in which the polarity of one of or both of the realpart and the imaginary part of Equation 10 are reversed. Bit b₁(t) is abit that contributes to the real part of modulated symbol S₁(t). Bitb₂(t) is a bit that contributes to the imaginary part of modulatedsymbol S₁(t).

Mapper 723 performs exclusive-OR between b₁(t) and the bit that mostcontributes to the real part of the second constellation among the bitsin the second bit stream inputted from interleaver 722. Mapper 723 alsoperforms exclusive-OR between b₂(t) and the bit that most contributes tothe imaginary part of the second constellation among the bits in thesecond bit stream inputted from interleaver 722. Mapper 723 then mapsthe second bit stream on which exclusive-OR has been performed, on thebasis of the second constellation.

Here, the bit that most contributes to the real part of the secondconstellation is a bit that causes the polarity of the real part of thesecond constellation to be reversed, for example, when the value of suchbit is reversed from 0 to 1 or from 1 to 0. Stated differently, the bitthat most contributes to the real part of the second constellationrefers to a bit that causes the negative/positive sign of the value ofthe real part of each modulated symbol to be reversed, for example, whenthe value of such bit is reversed from 0 to 1 or from 1 to 0.

Similarly, the bit that most contributes to the imaginary part of thesecond constellation is a bit that causes the polarity of the imaginarypart of the second constellation to be reversed, for example, when thevalue of such bit is reversed from 0 to 1 or from 1 to 0. Stateddifferently, the bit that most contributes to the imaginary part of thesecond constellation refers to a bit that causes the negative/positivesign of the value of the imaginary part of each modulated symbol to bereversed when the value of such bit is reversed from 0 to 1 or from 1 to0.

In the above description, mapper 723 converts the second bit stream,thereby substantially converting the second mapping scheme (the secondconstellation). However, mapper 723 may directly convert the secondmapping scheme (the second constellation) without converting the secondbit stream. Stated differently, mapper 723 may convert thecorrespondence between groups of bits and signal points in the secondconstellation.

Also, the conversion performed by mapper 723 may be performed by theconverter included in mapper 723.

As described above, the variation of superposition coding controls thepolarities of the real part and the imaginary part of each secondmodulated symbol in accordance with the values of the bits to be mappedonto the first modulated symbol that is superposed with such secondmodulated symbol. Note that the polarities of the real part and theimaginary part of each second modulated symbol may be controlled inaccordance with the first modulated symbol that is superposed with suchsecond modulated symbol. Also, the polarity of one of the real part andthe imaginary part of each second modulated symbol may be controlled, orthe polarities of both the real part and the imaginary part of eachsecond modulated symbol may be controlled.

<Sequential Decoding of Signal Obtained by Variation of SuperpositionCoding>

FIG. 16 shows an example configuration of reception device 800 capableof receiving and sequentially decoding the signal on which two dataseries are multiplexed onto two layers by the above-described variationof superposition coding, and capable of obtaining one of or both of themultiplexed two data series. The configuration and operation ofreception device 800 will be described with reference to FIG. 16.

Reception device 800 includes RF unit 830, demapper 811, deinterleaver812, decoder 813, encoder 814, interleaver 815, mapper 816, multiplier817, delayer 818, subtractor 819, converter 820, demapper 821,deinterleaver 822, and decoder 823. These structural components may alsobe implemented as dedicated or general-purpose circuits.

Demapper 811, deinterleaver 812, decoder 813, encoder 814, interleaver815, mapper 816, multiplier 817, delayer 818, subtractor 819, converter820, demapper 821, deinterleaver 822, and decoder 823 can also berepresented collectively as a derivation unit. RF unit 830 can also berepresented as a receiver. RF unit 830 may include an antenna.

Reception device 800 receives by an antenna the multiplexed signal sentfrom transmission device 500, 600, or 700, and inputs such multiplexedsignal into RF unit 830. Stated differently, RF unit 830 receives themultiplexed signal via the antenna. The multiplexed signal received byRF unit 830 is also represented as a received signal, and corresponds tothe superposed modulated symbol stream into which the first modulatedsymbol stream and the second modulated symbol stream are multiplexed. RFunit 830 generates a baseband received signal from the radio-frequencyreceived signal.

Demapper 811 demaps the baseband received signal on the basis of thefirst constellation of the first mapping scheme to generate the firstbit likelihood stream. For example, amplitude coefficient a₁ isreflected in the first constellation for demapping.

Deinterleaver 812 permutes the first bit likelihood stream on the basisof a permutation rule that is a reverse rule of the first permutationrule. Such permutation is also referred to as deinterleaving. Decoder813 performs decoding that is based on the first error control codingscheme by use of the first bit likelihood stream permuted bydeinterleaver 812, and outputs the decoding result as the first dataseries.

Here, of the received signal corresponding to the superposed modulatedsymbol stream, demapper 811 treats the components corresponding to thesecond modulated symbols in the second data series as an unknown signal(noise), and performs demapping on the basis of the first constellationof the first mapping scheme.

When only the first data series is to be obtained, reception device 800terminates the process upon completing the estimation of the first dataseries. Meanwhile, when the second data series is to be obtained inaddition to the first data series, or when only the second data seriesis to be obtained, reception device 800 performs the processes describedbelow to obtain the second data series.

Encoder 814 encodes the first data series obtained by decoder 813 on thebasis of the first error control coding scheme to generate the first bitstream. Interleaver 815 permutes the bits in the first bit streamgenerated by encoder 814 on the basis of the first permutation rule.Such permutation is also referred to as interleaving.

Mapper 816 maps the first bit stream permuted by interleaver 815 inaccordance with the first mapping scheme to generate the first modulatedsymbol stream that includes a plurality of first modulated symbols.Multiplier 817 multiplies the first modulated symbol stream outputted bymapper 816 by first amplitude coefficient a₁.

Delayer 818 delays the received signal outputted from RF unit 830 duringthe time from when RF unit 830 outputs the baseband received signal towhen multiplier 817 outputs the reproduced first modulated symbolstream.

Subtractor 819 subtracts, from the received signal delayed by delayer818, the first modulated symbol stream multiplied by first amplitudecoefficient a₁ by multiplier 817. Through this, subtractor 819 removesthe components corresponding to the first modulated symbols from thereceived signal on which the components corresponding to the firstmodulated symbols and the components and noise corresponding to thesecond modulated symbols are superposed. Subsequently, subtractor 819outputs a signal on which the components and noise corresponding to thesecond modulated symbols are superposed as a signal corresponding to thesecond modulated symbol stream.

Converter 820 converts the signal outputted from subtractor 819 as asignal corresponding to the second modulated symbol stream by use of thefirst bit stream reproduced through encoding, interleaving, etc.Demapper 821 demaps the signal outputted by converter 820 on the basisof the second constellation of the second mapping scheme to generate thesecond bit likelihood stream. For example, amplitude coefficient a₂ isreflected in the second constellation for demapping.

Deinterleaver 822 permutes the second bit likelihood stream on the basisof a permutation rule that is a reverse rule of the second permutationrule. Such permutation is also referred to as deinterleaving. Decoder823 decodes the second bit likelihood stream permuted by deinterleaver822 on the basis of the second error control coding scheme, and outputsthe decoding result as the second data series.

The following shows an example case in which QPSK is used as the firstmapping scheme to describe the operation of converter 820.

For example, when S₁(t) is the t-th modulated symbol in the firstmodulated symbol stream generated by mapper 816, and b₁(t) and b₂(t) area plurality of bits to be mapped onto S₁(t), modulated symbol S₁(t) isgiven by Equation 11.

$\begin{matrix}\left\lbrack {{Math}.\mspace{14mu} 11} \right\rbrack & \; \\{{S_{1}(t)} = \frac{\left( {{2 \cdot {b_{1}(t)}} - 1} \right) + {i \cdot \left( {{2 \cdot {b_{2}(t)}} - 1} \right)}}{\sqrt{2}}} & \left( {{Equation}\mspace{14mu} 11} \right)\end{matrix}$

Here, i denotes the imaginary unit. Modulated symbol S₁(t) may also begiven by an equation in which the polarity of one of or both of the realpart and the imaginary part of Equation 11 are reversed. Bit b₁(t) is abit that contributes to the real part of modulated symbol S₁(t). Bitb₂(t) is a bit that contributes to the imaginary part of modulatedsymbol S₁(t).

Converter 820 converts, into S′₂(t), signal S₂(t) corresponding to thet-th modulated symbol in the second modulated symbol stream out of thesignal outputted by subtractor 819, on the basis of b₁(t) and b₂(t) asshown by Equation 12.

[Math. 12]

S′ ₂(t)=(−1)^(b) ¹ ^((t)) ·Re[S ₂(t)]+i·(−1)^(b) ² ^((t)) ·Im[S₂(t)]  (Equation 12)

Here, S′₂(t) is the signal that has undergone the conversion. Also,Re[S₂(t)] is the value of the real part of S₂(t), and Im[S₂(t)] is thevalue of the imaginary part of S₂(t). Signal S′₂(t) that has undergonethe conversion may be given by an equation in which the polarity of oneof or both of the real part and the imaginary part of Equation 12 arereversed.

Through the above processes, reception device 800 obtains one of or bothof the first data series and the second data series from the signalreceived by the antenna.

FIG. 17 shows an example configuration of reception device 900 capableof receiving and sequentially decoding the signal on which two dataseries are multiplexed onto two layers by the above-described variationof superposition coding, and capable of obtaining one of or both of themultiplexed two data series. The configuration of reception device 900is different from the configuration of reception device 800. Theconfiguration and operation of reception device 900 will be describedwith reference to FIG. 17.

Reception device 900 includes RF unit 930, demapper 911, deinterleaver912, decoder 913, encoder 914, interleaver 915, mapper 916, multiplier917, delayer 918, subtractor 919, converter 920, demapper 921,deinterleaver 922, and decoder 923. These structural components may alsobe implemented as dedicated or general-purpose circuits.

Demapper 911, deinterleaver 912, decoder 913, encoder 914, interleaver915, mapper 916, multiplier 917, delayer 918, subtractor 919, converter920, demapper 921, deinterleaver 922, and decoder 923 can also berepresented collectively as a derivation unit. RF unit 930 can also berepresented as a receiver. RF unit 930 may include an antenna.

Reception device 900 receives by an antenna the multiplexed signal sentfrom transmission device 500, 600, or 700, and inputs such multiplexedsignal into RF unit 930. Stated differently, RF unit 930 receives themultiplexed signal via the antenna. The multiplexed signal received byRF unit 930 is also represented as a received signal, and corresponds tothe superposed modulated symbol stream into which the first modulatedsymbol stream and the second modulated symbol stream are multiplexed. RFunit 930 generates a baseband received signal from the radio-frequencyreceived signal.

Demapper 911 demaps the baseband received signal on the basis of thefirst constellation of the first mapping scheme to generate the firstbit likelihood stream. For example, amplitude coefficient a₁ isreflected in the first constellation for demapping.

Deinterleaver 912 permutes the first bit likelihood stream on the basisof a permutation rule that is a reverse rule of the first permutationrule. Such permutation is also referred to as deinterleaving. Decoder913 performs decoding that is based on the first error control codingscheme by use of the first bit likelihood stream permuted bydeinterleaver 912, and outputs the decoding result as the first dataseries.

Here, of the received signal corresponding to the superposed modulatedsymbol stream, demapper 911 treats the components corresponding to thesecond modulated symbols in the second data series as an unknown signal(noise), and performs demapping on the basis of the first constellationof the first mapping scheme.

When only the first data series is to be obtained, reception device 900terminates the process upon completing the estimation of the first dataseries. Meanwhile, when the second data series is to be obtained inaddition to the first data series, or when only the second data seriesis to be obtained, reception device 900 performs the processes describedbelow to obtain the second data series.

Encoder 914 encodes the first data series obtained by decoder 913 on thebasis of the first error control coding scheme to generate the first bitstream. Interleaver 915 permutes the bits in the first bit streamgenerated by encoder 914 on the basis of the first permutation rule.Such permutation is also referred to as interleaving.

Mapper 916 maps the first bit stream permuted by interleaver 915 inaccordance with the first mapping scheme to generate the first modulatedsymbol stream that includes a plurality of first modulated symbols.Multiplier 917 multiplies the first modulated symbol stream outputted bymapper 916 by first amplitude coefficient a₁.

Delayer 918 delays the received signal outputted from RF unit 930 duringthe time from when RF unit 930 outputs the baseband received signal towhen multiplier 917 outputs the reproduced first modulated symbolstream.

Subtractor 919 subtracts, from the received signal delayed by delayer918, the first modulated symbol stream multiplied by first amplitudecoefficient a₁ by multiplier 917. Through this, subtractor 919 removesthe components corresponding to the first modulated symbols from thereceived signal on which the components corresponding to the firstmodulated symbols and the components and noise corresponding to thesecond modulated symbols are superposed. Subsequently, subtractor 919outputs a signal on which the components and noise corresponding to thesecond modulated symbols are superposed as a signal corresponding to thesecond modulated symbol stream.

Converter 920 converts the signal outputted from subtractor 919 as asignal corresponding to the second modulated symbol stream by use of thefirst modulated symbol stream reproduced through encoding, interleaving,mapping, etc. Demapper 921 demaps the signal outputted by converter 920on the basis of the second constellation of the second mapping scheme togenerate the second bit likelihood stream. For example, amplitudecoefficient a₂ is reflected in the second constellation for demapping.

Deinterleaver 922 permutes the second bit likelihood stream on the basisof a permutation rule that is a reverse rule of the second permutationrule. Such permutation is also referred to as deinterleaving. Decoder923 decodes the second bit likelihood stream permuted by deinterleaver922 on the basis of the second error control coding scheme, and outputsthe decoding result as the second data series.

The following shows an example case in which QPSK is used as the firstmapping scheme to describe the operation of converter 920.

For example, when S₁(t) is the t-th modulated symbol in the firstmodulated symbol stream generated by mapper 916, and b₁(t) and b₂(t) area plurality of bits to be mapped onto S₁(t), modulated symbol S₁(t) isgiven by Equation 13.

$\begin{matrix}\left\lbrack {{Math}.\mspace{14mu} 13} \right\rbrack & \; \\{{S_{1}(t)} = \frac{\left( {{2 \cdot {b_{1}(t)}} - 1} \right) + {i \cdot \left( {{2 \cdot {b_{2}(t)}} - 1} \right)}}{\sqrt{2}}} & \left( {{Equation}\mspace{14mu} 13} \right)\end{matrix}$

Here, i denotes the imaginary unit. Modulated symbol S₁(t) may also begiven by an equation in which the polarity of one of or both of the realpart and the imaginary part of Equation 13 are reversed. Bit b₁(t) is abit that contributes to the real part of modulated symbol S₁(t). Bitb₂(t) is a bit that contributes to the imaginary part of modulatedsymbol S₁(t).

Converter 920 converts, into S′₂(t), signal S₂(t) corresponding to thet-th modulated symbol in the second modulated symbol stream out of thesignal outputted by subtractor 919, on the basis of modulated symbolS₁(t) as shown by Equation 14.

[Math. 14]

S′ ₂(t)=−sgn(Re[S ₁(t)])·Re[S ₂(t)]−i·sgn(Im[S ₁(t)])·Im[S ₂(t)]  (Equation 14)

Here, S′₂(t) is the signal that has undergone the conversion. Also,Re[S₂(t)] is the value of the real part of S₂(t), and Im[S₂(t)] is thevalue of the imaginary part of S₂(t). Also, sgn(Re[S₁(t)] is thepolarity of the real part of S₁(t), and sgn(Im[S₁(t)] is the polarity ofthe imaginary part of S₁(t). Signal S′₂(t) that has undergone theconversion may be given by an equation in which the polarity of one ofor both of the real part and the imaginary part of Equation 14 arereversed. Note that the conversion that is based on Equation 14 issubstantially the same as the conversion that is based on Equation 12.

Through the above processes, reception device 900 obtains one of or bothof the first data series and the second data series from the signalreceived by the antenna.

FIG. 18 shows an example configuration of reception device 1000 capableof receiving and sequentially decoding the signal on which two dataseries are multiplexed onto two layers by the above-described variationof superposition coding, and capable of obtaining one of or both of themultiplexed two data series. The configuration of reception device 1000is different from the configurations of reception devices 800 and 900.The configuration and operation of reception device 1000 will bedescribed with reference to FIG. 18.

Reception device 1000 includes RF unit 1030, demapper 1011,deinterleaver 1012, decoder 1013, encoder 1014, interleaver 1015, mapper1016, multiplier 1017, delayer 1018, subtractor 1019, demapper 1021,deinterleaver 1022, and decoder 1023. These structural components mayalso be implemented as dedicated or general-purpose circuits.

Demapper 1011, deinterleaver 1012, decoder 1013, encoder 1014,interleaver 1015, mapper 1016, multiplier 1017, delayer 1018, subtractor1019, demapper 1021, deinterleaver 1022, and decoder 1023 can also berepresented collectively as a derivation unit. RF unit 1030 can also berepresented as a receiver. RF unit 1030 may include an antenna. Demapper1021 may include a converter.

Reception device 1000 receives by an antenna the multiplexed signal sentfrom transmission device 500, 600, or 700, and inputs such multiplexedsignal into RF unit 1030. Stated differently, RF unit 1030 receives themultiplexed signal via the antenna. The multiplexed signal received byRF unit 1030 is also represented as a received signal, and correspondsto the superposed modulated symbol stream into which the first modulatedsymbol stream and the second modulated symbol stream are multiplexed. RFunit 1030 generates a baseband received signal from the radio-frequencyreceived signal.

Demapper 1011 demaps the baseband received signal on the basis of thefirst constellation of the first mapping scheme to generate the firstbit likelihood stream. For example, amplitude coefficient a₁ isreflected in the first constellation for demapping.

Deinterleaver 1012 permutes the first bit likelihood stream on the basisof a permutation rule that is a reverse rule of the first permutationrule. Such permutation is also referred to as deinterleaving. Decoder1013 performs decoding that is based on the first error control codingscheme by use of the first bit likelihood stream permuted bydeinterleaver 1012, and outputs the decoding result as the first dataseries.

Here, of the received signal corresponding to the superposed modulatedsymbol stream, demapper 1011 treats the components corresponding to thesecond modulated symbols in the second data series as an unknown signal(noise), and performs demapping on the basis of the first constellationof the first mapping scheme.

When only the first data series is to be obtained, reception device 1000terminates the process upon completing the estimation of the first dataseries. Meanwhile, when the second data series is to be obtained inaddition to the first data series, or when only the second data seriesis to be obtained, reception device 1000 performs the processesdescribed below to obtain the second data series.

Encoder 1014 encodes the first data series obtained by decoder 1013 onthe basis of the first error control coding scheme to generate the firstbit stream. Interleaver 1015 permutes the bits in the first bit streamgenerated by encoder 1014 on the basis of the first permutation rule.Such permutation is also referred to as interleaving.

Mapper 1016 maps the first bit stream permuted by interleaver 1015 inaccordance with the first mapping scheme to generate the first modulatedsymbol stream that includes a plurality of first modulated symbols.Multiplier 1017 multiplies the first modulated symbol stream outputtedby mapper 1016 by first amplitude coefficient a₁.

Delayer 1018 delays the received signal outputted from RF unit 1030during the time from when RF unit 1030 outputs the baseband receivedsignal to when multiplier 1017 outputs the reproduced first modulatedsymbol stream.

Subtractor 1019 subtracts, from the received signal delayed by delayer1018, the first modulated symbol stream multiplied by first amplitudecoefficient a₁ by multiplier 1017. Through this, subtractor 1019 removesthe components corresponding to the first modulated symbols from thereceived signal on which the components corresponding to the firstmodulated symbols and the components and noise corresponding to thesecond modulated symbols are superposed. Subsequently, subtractor 1019outputs a signal on which the components and noise corresponding to thesecond modulated symbols are superposed as a signal corresponding to thesecond modulated symbol stream.

Demapper 1021 demaps the signal outputted from subtractor 1019 as asignal corresponding to the second modulated symbol stream on the basisof the second constellation of the second mapping scheme to generate thesecond bit likelihood stream. Such process reflects the first bit streamreproduced through encoding, interleaving, etc. For example, amplitudecoefficient a₂ is reflected in the second constellation for demapping.

Deinterleaver 1022 permutes the second bit likelihood stream on thebasis of a permutation rule that is a reverse rule of the secondpermutation rule. Such permutation is also referred to asdeinterleaving. Decoder 1023 decodes the second bit likelihood streampermuted by deinterleaver 1022 on the basis of the second error controlcoding scheme, and outputs the decoding result as the second dataseries.

The following shows an example case in which QPSK is used as the firstmapping scheme to describe the operation of demapper 1021.

For example, when S₁(t) is the t-th modulated symbol in the firstmodulated symbol stream generated by mapper 1016, and b₁(t) and b₂(t)are a plurality of bits to be mapped onto S₁(t), modulated symbol S₁(t)is given by Equation 15.

$\begin{matrix}\left\lbrack {{Math}.\mspace{14mu} 15} \right\rbrack & \; \\{{S_{1}(t)} = \frac{\left( {{2 \cdot {b_{1}(t)}} - 1} \right) + {i \cdot \left( {{2 \cdot {b_{2}(t)}} - 1} \right)}}{\sqrt{2}}} & \left( {{Equation}\mspace{14mu} 15} \right)\end{matrix}$

Here, i denotes the imaginary unit. Modulated symbol S₁(t) may also begiven by an equation in which the polarity of one of or both of the realpart and the imaginary part of Equation 15 are reversed. Bit b₁(t) is abit that contributes to the real part of modulated symbol S₁(t). Bitb₂(t) is a bit that contributes to the imaginary part of modulatedsymbol S₁(t).

Demapper 1021 demaps signal S₂(t) outputted from subtractor 1019 as asignal corresponding to the t-th modulated symbol in the secondmodulated symbol stream on the basis of the second constellation of thesecond mapping scheme.

Demapper 1021 reverses the bit likelihood corresponding to the bit thatmost contributes to the real part of the second constellation inaccordance with b₁(t) among the bit likelihoods in the bit likelihoodstream obtained by demapping. Demapper 1021 also reverses the bitlikelihood corresponding to the bit that most contributes to theimaginary part of the second constellation in accordance with b₂(t)among the bit likelihoods in the bit likelihood stream obtained bydemapping.

For example, demapper 1021 performs exclusive-OR between b₁(t) and thebit likelihood corresponding to the bit that most contributes to thereal part of the second constellation among the bit likelihoods in thebit likelihood stream obtained by demapping. Demapper 1021 also performsexclusive-OR between b₂(t) and the bit likelihood corresponding to thebit that most contributes to the imaginary part of the secondconstellation among the bit likelihoods in the bit likelihood streamobtained by demapping.

Demapper 1021 then outputs the bit likelihood stream that has undergonethe above-described reversal processes as the second bit likelihoodstream.

In the above description, demapper 1021 converts the bit likelihoodstream, thereby substantially converting the second mapping scheme (thesecond constellation). However, demapper 1021 may directly convert thesecond mapping scheme (the second constellation) without converting thebit likelihood stream. Stated differently, demapper 1021 may convert thecorrespondence between groups of bits and signal points in the secondconstellation.

Also, the conversion performed by demapper 1021 may be performed by theconverter included in demapper 1021.

Through the above processes, reception device 1000 obtains one of orboth of the first data series and the second data series from the signalreceived by the antenna.

<Parallel Decoding of Signal Obtained by Variation of SuperpositionCoding>

The following describes a reception method for parallel decoding of asignal obtained by the variation of superposition coding according tothe present embodiment. The configuration of the transmission device isthe same as the configuration of transmission device 500 shown in FIG.13, transmission device 600 shown in FIG. 14, or transmission device 700shown in FIG. 15, and thus will not be described. In parallel decodingin the variation of superposition coding, the reception device treatsthe components of the modulated symbol stream in the first layer as anunknown signal (noise) to decode the second layer, without removing thecomponents of the modulated symbol stream in the first layer included inthe received signal.

FIG. 19 shows an example configuration of reception device 1100 capableof receiving and performing parallel decoding on the signal on which twodata series are multiplexed onto two layers by the variation ofsuperposition coding, and capable of obtaining one of or both of themultiplexed two data series. The configuration and operation ofreception device 1100 will be described with reference to FIG. 19.

Reception device 1100 includes RF unit 1130, demapper 1110,deinterleaver 1112, decoder 1113, deinterleaver 1122, and decoder 1123.These structural components may also be implemented as dedicated orgeneral-purpose circuits. Demapper 1110, deinterleaver 1112, decoder1113, deinterleaver 1122, and decoder 1123 can also be representedcollectively as a derivation unit. RF unit 1130 can also be representedas a receiver. RF unit 1130 may include an antenna.

Reception device 1100 receives by an antenna the multiplexed signal sentfrom transmission device 500, 600, or 700, and inputs such multiplexedsignal into RF unit 1130. Stated differently, RF unit 1130 receives themultiplexed signal via the antenna. The multiplexed signal received byRF unit 1130 is also represented as a received signal. RF unit 1130generates a baseband received signal from the radio-frequency receivedsignal.

Demapper 1110 demaps the baseband received signal to generate the firstbit likelihood stream and the second bit likelihood stream. For example,demapper 1110 performs demapping on the basis of a variationsuperposition constellation that shows the arrangement of signal pointsof superposed modulated symbols obtained by superposing the firstmodulated symbols and the second modulated symbols by the variation ofsuperposition coding.

The variation superposition constellation is determined in accordancewith the first constellation of the first mapping scheme, the secondconstellation of the second mapping scheme, first amplitude coefficienta₁, second amplitude coefficient a₂, etc.

FIG. 20 shows the variation superposition constellation that supportsthe variation of superposition coding. More specifically, the variationsuperposition constellation is a combination of the QPSK constellationshown in FIG. 4 and the Nu-256QAM constellation shown in FIG. 5.

Even more specifically, the Nu-256QAM constellation (256 signal points)is placed on each of the four regions in the complex plane in accordancewith the four signal points of the QPSK constellation. These fourregions, each corresponding to Nu-256QAM constellation, may partiallyoverlap with each other. The present variation superpositionconstellation reflects the conversion performed on the second modulatedsymbol stream.

For example, when the Nu-256QAM constellation is combined with a signalpoint with a positive real part among the four signal points of the QPSKconstellation, the polarity of the real part of the Nu-256QAMconstellation is reversed. Also, for example, when the Nu-256QAMconstellation is combined with a signal point with a positive imaginarypart among the four signal points of the QPSK constellation, thepolarity of the imaginary part of the Nu-256QAM constellation isreversed.

More specifically, a first signal point, a second signal point, a thirdsignal point, a fourth signal point, a fifth signal point, and a sixthsignal point are shown in FIG. 20. When the polarity of the real part ofthe Nu-256QAM constellation is not reversed, the first signal point andthe third signal point correspond to the same bit values of the secondbit stream. Similarly, when the polarity of the imaginary part of theNu-256QAM constellation is not reversed, the fourth signal point and thesixth signal point correspond to the same bit values of the second bitstream.

When the polarity of the real part of the Nu-256QAM constellation isreversed, the first signal point and the second signal point correspondto the same bit values of the second bit stream. Also, when the polarityof the imaginary part of the Nu-256QAM constellation is reversed, thefourth signal point and the fifth signal point correspond to the samebit values of the second bit stream. Stated differently, such reversalenables a plurality of signal points that correspond to the same bitvalues of the second bit stream to approach each other and converge.This mitigates the effect of noise on demapping.

Demapper 1110 performs demapping on the basis of the variationsuperposition constellation as shown in FIG. 20. Stated differently,demapper 1110 generates the first bit likelihood stream with themodulated symbol stream of the second layer remaining unknown, andgenerates the second bit likelihood stream with the modulated symbolstream of the first layer remaining unknown.

Note that demapper 1110 may use the first constellation of the firstmapping scheme to generate the first bit likelihood stream, and may usethe above-described variation superposition constellation to generatethe second bit likelihood stream.

The first constellation, when used to generate the first bit likelihoodstream, enables demapper 1110 to reduce the number of signal points thatshould be considered in generating the first bit likelihood stream,compared to when the variation superposition constellation is also usedto generate the first bit likelihood stream. This thus enables demapper1110 to reduce the number of arithmetic computations.

Demapper 1110 corresponds, for example, to the first demapper thatdemaps the received signal to generate the first bit likelihood streamand the second demapper that demaps the received signal to generate thesecond bit likelihood stream. Demapper 1110 may include the firstdemapper that demaps the received signal to generate the first bitlikelihood stream and the second demapper that demaps the receivedsignal to generate the second bit likelihood stream.

Demapper 1110 may convert the second bit likelihood stream that isgenerated using not the variation superposition constellation but thesuperposition constellation, in accordance with the first bit likelihoodstream. This enables demapper 1110 to obtain the same second bitlikelihood stream as the second bit likelihood stream that is generatedusing the variation superposition constellation.

Demapper 1110 may convert the multiplexed signal without using thevariation superposition constellation to obtain the same second bitlikelihood stream as the second bit likelihood stream that is generatedusing the variation superposition constellation.

Deinterleaver 1112 permutes the first bit likelihood stream on the basisof a permutation rule that is a reverse rule of the first permutationrule. Such permutation is also referred to as deinterleaving. Decoder1113 decodes the first bit likelihood stream permuted by deinterleaver1112 on the basis of the first error control coding scheme, and outputsthe decoding result as the first data series.

Deinterleaver 1122 permutes the second bit likelihood stream on thebasis of a permutation rule that is a reverse rule of the secondpermutation rule. Such permutation is also referred to asdeinterleaving. Decoder 1123 decodes the second bit likelihood streampermuted by deinterleaver 1122 on the basis of the second error controlcoding scheme, and outputs the decoding result as the second dataseries.

Through the above processes, reception device 1100 obtains one of orboth of the first data series and the second data series from the signalreceived by the antenna.

Note that transmission devices 500, 600, and 700, and reception devices800, 900, 1000, and 1100 may omit permutation (interleaving anddeinterleaving) as in the case of Embodiment 1. Stated differently,their respective interleavers and deinterleavers are optional structuralcomponents, and thus may not be included in these devices.

Interleaving and deinterleaving, however, make a pair. As such, whentransmission devices 500, 600, and 700 include their respectiveinterleavers, reception devices 800, 900, 1000, and 1100 basicallyinclude their respective deinterleavers and interleavers. Meanwhile,when transmission devices 500, 600, and 700 do not include theirrespective interleavers, reception devices 800, 900, 1000, and 1100 donot include their respective deinterleavers and interleavers.

Amplitude coefficient a₁ may be reflected in the mapping for generatingthe first modulated symbols performed in reception devices 800, 900, and1000. In such a case, the multiplication of amplitude coefficient a₁ maybe omitted. Reception devices 800, 900, and 1000 thus may not includemultipliers 817, 917, and 1017, respectively.

Error control coding on the first data series and the second data seriesmay be performed by an external device. In such a case, transmissiondevices 500, 600, and 700 may omit error control coding, and may notinclude encoders 511, 521, 611, 621, 711, and 721.

FIG. 21 is a flowchart of example operations performed by transmissiondevice 500. First, mapper 513 maps the first bit stream of the firstdata series to generate the first modulated symbol stream of the firstdata series (S301). Then, mapper 523 maps the second bit stream of thesecond data series to generate the second modulated symbol stream of thesecond data series (S302).

Converter 525 subjects the second modulated symbol stream to conversionin accordance with the first modulation symbol stream (S303). Morespecifically, converter 525 converts the second modulated symbol streamin accordance with the first bit stream, thereby subjecting the secondmodulated symbol stream to conversion in accordance with the firstmodulated symbol stream.

Next, the superposition unit constituted by first multiplier 514, secondmultiplier 524, and adder 530 superposes the first modulated symbolstream and the second modulated symbol stream that has been subjected toconversion in accordance with the first modulated symbol stream at apredetermined amplitude ratio, thereby generating the multiplexed signal(S304). RF unit 540 then sends the generated multiplexed signal (S305).

Note that in the above operation example, transmission device 500converts the second modulated symbol stream in accordance with the firstbit stream, thereby subjecting the second modulated symbol stream toconversion in accordance with the first modulated symbol stream (S303).Alternatively, transmission device 500 may convert the second modulatedsymbol stream in accordance with the first modulated symbol stream, asin the case of transmission device 600, thereby subjecting the secondmodulated symbol stream to conversion in accordance with the firstmodulated symbol stream.

Alternatively, as in the case of transmission device 700, transmissiondevice 500 may convert the second bit stream or the second mappingscheme (the second constellation) used to generate the second modulatedsymbol stream, in accordance with the first bit stream. Through this,the second modulated symbol stream may be subjected to conversion inaccordance with the first modulated symbol stream. In such a case, thesecond bit stream or the second mapping scheme is converted before thesecond modulated symbol stream is generated.

Stated differently, the second bit stream, the second mapping scheme, orthe second modulated symbol stream may be converted in accordance withthe first bit stream or the first modulated symbol stream, therebysubjecting the second modulated symbol stream to conversion inaccordance with the first modulated symbol stream.

Converter 525 may subject the second modulated symbol stream toconversion in accordance with the first modulated symbol stream, therebycontrolling the polarities of the real part and the imaginary part ofeach modulated symbol in the second modulated symbol stream. Throughthis, converter 525 may reverse the polarity of the real part of eachsecond modulated symbol when the real part of the corresponding firstmodulated symbol satisfies a predetermined real part condition, and mayreverse the polarity of the imaginary part of each second modulatedsymbol when the imaginary part of the corresponding first modulatedsymbol satisfies a predetermined condition.

The predetermined real part condition may be a condition that thepolarity of the real part should be a predetermined polarity of the realpart, or may be a condition that the real part should be within apredetermined range of the real part greater than or equal to one. Thepredetermined range of the real part greater than or equal to one may bea positive range or a negative range. Similarly, the predeterminedimaginary part condition may be a condition that the polarity of theimaginary part should be a predetermined polarity of the imaginary part,or may be a condition that the imaginary part should be within apredetermined range of the imaginary part greater than or equal to one.The predetermined range of the imaginary part greater than or equal toone may be a positive range or a negative range.

FIG. 22 is a flowchart of example operations performed by receptiondevices 800, 900, 1000, and 1100. First, the receiver receives themultiplexed signal (S401). Here, the receiver is RF unit 830 ofreception device 800, RF unit 930 of reception device 900, RF unit 1030of reception device 1000, or RF unit 1130 of reception device 1100.

The multiplexed signal is a signal into which a plurality of data seriesincluding the first data series in the first layer and the second dataseries in the second layer are multiplexed. The multiplexed signal isalso a signal on which the first modulated symbol stream and the secondmodulated symbol stream are superposed at a predetermined amplituderatio.

The first modulated symbol stream is a modulated symbol stream that isgenerated by mapping the first bit stream of the first data series. Thesecond modulated symbol stream is a modulated symbol stream that isgenerated by mapping the second bit stream of the second data series,and that has been subjected to conversion in accordance with the firstmodulated symbol stream.

Next, the derivation unit derives at least one of the first data seriesand the second data series from the multiplexed signal (S402).

The derivation unit of reception device 800 is constituted, for example,by demapper 811, deinterleaver 812, decoder 813, encoder 814,interleaver 815, mapper 816, multiplier 817, delayer 818, subtractor819, converter 820, demapper 821, deinterleaver 822, and decoder 823.

The derivation unit of reception device 900 is constituted, for example,by demapper 911, deinterleaver 912, decoder 913, encoder 914,interleaver 915, mapper 916, multiplier 917, delayer 918, subtractor919, converter 920, demapper 921, deinterleaver 922, and decoder 923

The derivation unit of reception device 1000 is constituted, forexample, by demapper 1011, deinterleaver 1012, decoder 1013, encoder1014, interleaver 1015, mapper 1016, multiplier 1017, delayer 1018,subtractor 1019, demapper 1021, deinterleaver 1022, and decoder 1023

The derivation unit of reception device 1100 is constituted, forexample, by demapper 1110, deinterleaver 1112, decoder 1113,deinterleaver 1122, and decoder 1123.

In accordance with the above operations, the multiplexed signal isreceived into which the first modulated symbol stream and the secondmodulated symbol stream that has been subjected to conversion inaccordance with the first modulated symbol stream are multiplexed. Then,at least one of the first data series and the second data series isderived from such multiplexed signal. Stated differently, suchconfiguration enables: the reception of the multiplexed signal that hasbeen superposed in such a manner that reduces performance degradation atthe time of parallel decoding: and an efficient derivation of one of orboth of the first data series and the second data series from suchmultiplexed signal.

Reception device 1100 as shown in FIG. 19 that performs paralleldecoding has lower performance in decoding the second layer than that ofreception devices 800, 900, and 1000 as shown in FIG. 16, FIG. 17, andFIG. 18 that perform sequential decoding.

FIG. 23 shows an example simulation result of the transmission capacityof the second layer when the ratio between signal power P_(s1) of thefirst layer and signal power P_(s2) of the second layer isP_(s1):P_(s2)=2:1. In FIG. 23, the lateral axis represents as dB(decibel) the ratio of signal power P_(s) to noise power P_(n) (SNR),and the vertical axis represents transmission capacity. In FIG. 23, thesolid line indicates the transmission capacity of the second layer whensequential decoding is performed, and the broken line indicates thetransmission capacity of the second layer when parallel decoding isperformed.

As FIG. 23 shows, in the decoding of the second layer, parallel decodinginvolves an increased SNR with respect to the same transmission capacityand a decreased transmission capacity with respect to the same SNR,compared to sequential decoding.

As described above, reception device 1100 according to the presentembodiment that performs parallel decoding has lower performance indecoding the second data series transmitted on the second layer thanthat of reception devices 800, 900, and 1000 that perform sequentialdecoding. However, reception device 1100 reduces the number ofstructural components required to decode the second layer.

More specifically, reception device 1100 eliminates the need for thestructural components that are required by reception devices 800, 900,and 1000 shown in FIG. 16, FIG. 17, and FIG. 18 performing sequentialdecoding to reproduce the modulated symbol stream of the first layer.Stated differently, encoders 814, 914, and 1014, interleavers 815, 915,and 1015, mappers 816, 916, and 1016, and multipliers 817, 917, and 1017are not required.

Reception device 1100 also eliminates the need for delayers 818, 918,and 1018 that delay the received signal, and subtractors 819, 919, and1019 that remove the components of the modulated symbols in the firstlayer reproduced from the received signal.

The circuit size can be thus reduced. Reception device 1100 alsorequires a smaller number of arithmetic computations and lower powerconsumption than are required by reception devices 800, 900, and 1000.

Reception devices 800, 900, and 1000 shown in FIG. 16, FIG. 17, and FIG.18 that perform sequential decoding demodulate the first layer in thereceived signal to obtain the first data series, and generate the firstmodulated symbol stream from the obtained first data series.Subsequently, reception devices 800, 900, and 1000 start demodulatingthe second layer in the received signal to obtain the second dataseries.

Meanwhile, reception device 1100 according to the present embodimentthat performs parallel decoding is capable of simultaneously obtainingthe first data series and the second data series in parallel, therebyreducing processing delays.

The reception device may observe the SNR of the received signal to makeselection between parallel decoding to be performed when the SNR is highand sequential decoding to be performed when the SNR is low.

In such a case, reception device 800 shown in FIG. 16 includes, forexample, a controller that makes selection between sequential decodingand parallel decoding depending on the SNR. Such controller may beincluded in RF unit 830 or demapper 821. Furthermore, demapper 821 isconfigured to perform demapping based on the variation superpositionconstellation, which is described as an operation performed by demapper1110 shown in FIG. 19, in addition to demapping that is based on thesecond constellation.

Demapper 821 switches between demapping to be performed on the signaloutputted from converter 820 on the basis of the second constellationand demapping to be performed on the signal outputted from RF unit 830on the basis of the variation superposition constellation. For example,demapper 821 switches between these demapping operations in accordancewith a control signal from the controller.

Note that such configuration is also obtained by a combination ofreception device 400 shown in FIG. 11, reception device 800 (converter820, demapper 821, etc.) shown in FIG. 16, and reception device 1100(demapper 1110, etc.) shown in FIG. 19.

Another configuration is that reception device 900 shown in FIG. 17includes, for example, a controller that makes selection betweensequential decoding and parallel decoding depending on the SNR. Suchcontroller may be included in RF unit 930 or demapper 921. Furthermore,demapper 921 is configured to perform demapping based on the variationsuperposition constellation, which is described as an operationperformed by demapper 1110 shown in FIG. 19, in addition to demappingthat is based on the first bit stream and the second constellation.

Demapper 921 switches between demapping to be performed on the signaloutputted from converter 920 on the basis of the second constellationand demapping to be performed on the signal outputted from RF unit 930on the basis of the variation superposition constellation. For example,demapper 921 switches between these demapping operations in accordancewith a control signal from the controller.

Note that such configuration is also obtained by a combination ofreception device 400 shown in FIG. 11, reception device 900 (converter920, demapper 921, etc.) shown in FIG. 17, and reception device 1100(demapper 1110, etc.) shown in FIG. 19.

Still another configuration is that reception device 1000 shown in FIG.18 includes, for example, a controller that makes selection betweensequential decoding and parallel decoding depending on the SNR. Suchcontroller may be included in RF unit 1030 or demapper 1021.Furthermore, demapper 1021 is configured to perform demapping based onthe variation superposition constellation, which is described as anoperation performed by demapper 1110 shown in FIG. 19, in addition todemapping that is based on the first bit stream and the secondconstellation.

Demapper 1021 switches between demapping to be performed on the signaloutputted from subtractor 1019 on the basis of the second constellationand demapping to be performed on the signal outputted from RF unit 1030on the basis of the variation superposition constellation. For example,demapper 1021 switches between these demapping operations in accordancewith a control signal from the controller.

Note that such configuration is also obtained by a combination ofreception device 400 shown in FIG. 11, reception device 1000 (demapper1021, etc.) shown in FIG. 18, and reception device 1100 (demapper 1110,etc.) shown in FIG. 19.

As described above, reception devices 800, 900, and 1000 performparallel decoding when the SNR is high, thereby reducing the number ofarithmetic computations and power consumption. Reception devices 800,900, and 1000 also perform parallel decoding when the SNR is high,thereby reducing processing delays. Meanwhile, reception devices 800,900, and 1000 perform sequential decoding when the SNR is low, therebyincreasing the possibility of correctly decoding the second data series.

Comparison between the transmission capacity in the multiplexing schemeutilizing superposition coding shown in FIG. 10 and the transmissioncapacity in the multiplexing scheme utilizing the variation ofsuperposition coding shown in FIG. 23 presents the findings describedbelow.

The characteristics of the transmission capacities exhibited bysequential decoding (indicated by the solid line) are the same betweenthe multiplexing scheme utilizing superposition coding (FIG. 10) and themultiplexing scheme utilizing the variation of superposition coding(FIG. 23). Meanwhile, the characteristics of the transmission capacitiesexhibited by parallel decoding (indicated by the broken line) areimproved by use of the multiplexing scheme utilizing the variation ofsuperposition coding (FIG. 23) compared to the multiplexing schemeutilizing the superposition coding (FIG. 10). Stated differently, themultiplexing scheme utilizing the variation of superposition codingprovides desirable results both in sequential decoding and paralleldecoding.

As described above, the reception device according to one aspect of thepresent disclosure is a reception device that receives a multiplexedsignal into which a plurality of data series have been multiplexed bysuperposition coding, and derives the plurality of data series from themultiplexed signal, the plurality of data series including a first dataseries in a first layer and a second data series in a second layer. Suchreception device includes: a receiver that receives the multiplexedsignal; a first demapper that demaps the multiplexed signal, with asecond modulated symbol stream of the second data series being includedin the multiplexed signal as an undefined signal component, to generatea first bit likelihood stream of the first data series; a seconddemapper that demaps the multiplexed signal, with a first modulatedsymbol stream of the first data series being included in the multiplexedsignal as an undefined signal component, to generate a second bitlikelihood stream of the second data series; a first decoder thatperforms error control decoding on the first bit likelihood stream toderive the first data series; and a second decoder that performs errorcontrol decoding on the second bit likelihood stream to derive thesecond data series.

This enables the reception device to derive the second data serieswithout waiting for the derivation, etc. of the first data series. Thereception device thus can reduce processing delays. Stated differently,the reception device is capable of efficiently performing processing ina multiplexing scheme that utilizes superposition coding.

For example, the multiplexed signal received by the receiver may be asignal on which the first modulated symbol stream and the secondmodulated symbol stream are superposed at a predetermined amplituderatio, and in which a polarity of a real part and a polarity of animaginary part of each modulated symbol in the second modulated symbolstream are controlled in accordance with the first modulated symbolstream, the first modulated symbol stream being generated by mapping afirst bit stream of the first data series, the second modulated symbolstream being generated by mapping a second bit stream of the second dataseries.

This enables the reception device to receive a multiplexed signal of thefirst modulated symbol stream and the second modulated symbol streamthat has been adjusted in accordance with the first modulated symbolstream. This thus enables the reception device to appropriately derivethe first data series and the second data series from the multiplexedsignal into which the first data series and the second data series areappropriately multiplexed.

For example, the multiplexed signal received by the receiver may be asignal on which a first modulated symbol in the first modulated symbolstream and a second modulated symbol in the second modulated symbolstream are superposed, and in which the polarity of the real part of thesecond modulated symbol is subjected to a reversal when a real part ofthe first modulated symbol satisfies a predetermined real part conditionand the polarity of the imaginary part of the second modulated symbol issubjected to a reversal when an imaginary part of the first modulatedsymbol satisfies a predetermined imaginary part condition.

This enables the reception device to receive, as the multiplexed signal,a signal on which the first modulated symbol and the second modulatedsymbol, a polarity of which has been reversed in accordance with thefirst modulated symbol, are superposed. The reversal of a polarity ofthe second modulated symbol enables a plurality of signal points thatare associated with the same group of bits in the second data series toapproach each other. The reception device is thus capable ofappropriately generating the second modulated symbol stream from themultiplexed signal that includes the first modulated symbol stream.

For example, the second demapper may demap the multiplexed signal togenerate the second bit likelihood stream, based on a superpositionconstellation that is a combination of a first constellation used to mapthe first bit stream and a second constellation used to map the secondbit stream, and that reflects the reversal of the polarity of the realpart of the second modulated symbol and the reversal of the polarity ofthe imaginary part of the second modulated symbol.

This enables the reception device to appropriately generate the secondmodulated symbol stream from the multiplexed signal on the basis of thesuperposition constellation in which a plurality of signal pointsassociated with the same group of bits come close to each other.

For example, the reception device may further include: an encoder thatperforms error control coding on the first data series derived by thefirst decoder to generate a first bit stream of the first data series; amapper that maps the first bit stream to generate the first modulatedsymbol stream; a delayer that delays the multiplexed signal received bythe receiver for a predetermined time length; and a subtractor thatsubtracts the first modulated symbol stream from the multiplexed signaldelayed by the delayer. The second demapper may demap the multiplexedsignal, with the first modulated symbol stream being included in themultiplexed signal as an undefined signal component, to generate thesecond bit likelihood stream, when a signal-to-noise ratio of themultiplexed signal satisfies a predetermined requirement, and may demapthe multiplexed signal from which the first modulated symbol stream hasbeen subtracted to generate the second bit likelihood stream, when thesignal-to-noise ratio of the multiplexed signal fails to satisfy thepredetermined requirement.

This allows operations to be selectively switched, depending on thesignal-to-noise ratio, between generating the second modulated symbolstream form the multiplexed signal from which the first modulated symbolstream remains unremoved and generating the second modulated symbolstream from the multiplexed signal from which the first modulated symbolstream has been removed. This thus enables the reception device toprevent extreme decrease, etc. in the transmission capacity.

The reception method according to another aspect of the presentdisclosure is a reception method of receiving a multiplexed signal intowhich a plurality of data series have been multiplexed by superpositioncoding, and deriving the plurality of data series from the multiplexedsignal, the plurality of data series including a first data series in afirst layer and a second data series in a second layer. Such receptionmethod includes: receiving the multiplexed signal; demapping themultiplexed signal, with a second modulated symbol stream of the seconddata series being included in the multiplexed signal as an undefinedsignal component, to generate a first bit likelihood stream of the firstdata series; demapping the multiplexed signal, with a first modulatedsymbol stream of the first data series being included in the multiplexedsignal as an undefined signal component, to generate a second bitlikelihood stream of the second data series; performing error controldecoding on the first bit likelihood stream to derive the first dataseries; and performing error control decoding on the second bitlikelihood stream to derive the second data series.

This enables a reception device, etc. employing this reception method toderive the second data series without waiting for the derivation, etc.of the first data series. The reception device, etc. employing thisreception method thus can reduce processing delays. Stated differently,the reception device, etc. employing this reception method is capable ofefficiently performing processing in a multiplexing scheme that utilizessuperposition coding.

For example, the multiplexed signal may be a signal on which the firstmodulated symbol stream and the second modulated symbol stream aresuperposed at a predetermined amplitude ratio, and in which a polarityof a real part and a polarity of an imaginary part of each modulatedsymbol in the second modulated symbol stream are controlled inaccordance with the first modulated symbol stream, the first modulatedsymbol stream being generated by mapping a first bit stream of the firstdata series, the second modulated symbol stream being generated bymapping a second bit stream of the second data series.

This enables the reception device, etc. employing this reception methodto receive a multiplexed signal of the first modulated symbol stream andthe second modulated symbol stream that has been adjusted in accordancewith the first modulated symbol stream. This thus enables the receptiondevice, etc. employing this reception method to appropriately derive thefirst data series and the second data series from the multiplexed signalinto which the first data series and the second data series areappropriately multiplexed.

For example, the multiplexed signal may be a signal on which a firstmodulated symbol in the first modulated symbol stream and a secondmodulated symbol in the second modulated symbol stream are superposed,and in which the polarity of the real part of the second modulatedsymbol is subjected to a reversal when a real part of the firstmodulated symbol satisfies a predetermined real part condition and thepolarity of the imaginary part of the second modulated symbol issubjected to a reversal when an imaginary part of the first modulatedsymbol satisfies a predetermined imaginary part condition.

This enables the reception device, etc. employing this reception methodto receive, as the multiplexed signal, a signal on which the firstmodulated symbol and the second modulated symbol, a polarity of whichhas been reversed in accordance with the first modulated symbol, aresuperposed. The reversal of a polarity of the second modulated symbolenables a plurality of signal points that are associated with the samegroup of bits in the second data series to approach each other. Thereception device, etc. employing this reception method is thus capableof appropriately generating the second modulated symbol stream from themultiplexed signal that includes the first modulated symbol stream.

For example, in the generating of the second bit likelihood stream, themultiplexed signal may be demapped to generate the second bit likelihoodstream, based on a superposition constellation that is a combination ofa first constellation used to map the first bit stream and a secondconstellation used to map the second bit stream, and that reflects thereversal of the polarity of the real part of the second modulated symboland the reversal of the polarity of the imaginary part of the secondmodulated symbol.

This enables the reception device, etc. employing this reception methodto appropriately generate the second modulated symbol stream from themultiplexed signal on the basis of the superposition constellation inwhich a plurality of signal points associated with the same groups ofbits come close to each other.

For example, the reception method may further include: performing errorcontrol coding on the first data series that has been derived togenerate a first bit stream of the first data series; mapping the firstbit stream to generate the first modulated symbol stream; delaying themultiplexed signal that has been received for a predetermined timelength; and subtracting the first modulated symbol stream from themultiplexed signal that has been delayed. In the generating of thesecond bit likelihood stream, the multiplexed signal may be demapped,with the first modulated symbol stream being included in the multiplexedsignal as an undefined signal component, to generate the second bitlikelihood stream, when a signal-to-noise ratio of the multiplexedsignal satisfies a predetermined requirement, and the multiplexed signalfrom which the first modulated symbol stream has been subtracted may bedemapped to generate the second bit likelihood stream, when thesignal-to-noise ratio of the multiplexed signal fails to satisfy thepredetermined requirement.

This allows operations to be selectively switched, depending on thesignal-to-noise ratio, between generating the second modulated symbolstream form the multiplexed signal from which the first modulated symbolstream remains unremoved and generating the second modulated symbolstream from the multiplexed signal from which the first modulated symbolstream has been removed. This thus enables the reception device, etc.employing this reception method to prevent extreme decrease, etc. in thetransmission capacity.

Note that although the above description of the embodiments illustratesan example in which two data series are multiplexed and transmitted onthe two layers to simplify the description, it is clear that the presentdisclosure is readily extendable to multiplexing and transmitting threeor more data series, following the embodiments.

Also, FIG. 1, and FIG. 13 to FIG. 15 illustrate an example in which aradio-frequency signal is sent from an external antenna connected to thetransmission device that does not include an antenna, but thetransmission device may include an antenna such that a radio-frequencysignal is sent from such antenna of the transmission device. Also, FIG.2, FIG. 7, and FIG. 16 to FIG. 19 illustrate an example in which aradio-frequency signal is sent from an external antenna connected to thereception device that does not include an antenna, but the receptiondevice may include an antenna such that a radio-frequency signal is sentfrom such antenna of the reception device.

Also, the antennas used to send/receive a radio-frequency signal may bean antenna unit that includes a plurality of antennas.

Although not illustrated in FIG. 1, and FIG. 13 to FIG. 15, thetransmission device may include a frame configuration unit that arrangesa superposed signal generated by the adder in accordance with apredetermined frame configuration to generate a frame, and outputs suchframe into the RF unit.

Here, the configuration of a frame generated by the frame configurationunit may be uniform, or may be changed in accordance with a controlsignal sent from a controller not illustrated. The frame configurationunit arranges, in a frame, a superposed modulated symbol stream in whichthe first data series and the second data series are multiplexed, inaccordance with a predetermined rule.

The frame generated by the frame configuration unit may include a pilotsymbol, a control information symbol, a preamble, etc. in addition to adata symbol. Note that a pilot symbol, a control information symbol, anda preamble can each be referred to by another name.

For example, a pilot symbol may be a symbol that is generated by mappinga bit stream known to the reception device on the basis of PSKmodulation such as BPSK and QPSK. A pilot symbol may also be a symbolthat includes an amplitude and in-phase (or complex value) known to thereception device. A pilot symbol may also be a symbol, according towhich the reception device can estimate the amplitude and in-phase (orcomplex value) sent by the transmission device.

Then, the reception device uses the pilot symbol to perform frequencysynchronization, time synchronization, channel estimation, etc. on thereceived signal. Channel estimation is also referred to as theestimation of channel state information (CSI).

A control information symbol is a symbol used to transmit informationthat should be notified to the reception device as information requiredto demodulate a received signal and obtain a desired data series.

For example, the transmission device sends a control information symbolcorresponding to control information. The control information mayindicate the mapping (modulation) scheme and error control coding schemeused for each data series, the code rate and code length of the errorcontrol coding scheme, and the positions where the modulated symbols ofeach data series are arranged in a frame, etc. The reception devicedemodulates the control information symbol to obtain the controlinformation. The reception device then demodulates a data symbol on thebasis of the obtained control information to obtain the data series.

The control information may also include information used to control theoperations of an application, such as settings information for an upperlayer.

A preamble is a signal added at the top of a frame. For example, thereception device may receive a signal that includes a preamble toperform processes such as frame detection and frame synchronization onthe basis of the preamble. A preamble may also include a pilot symboland a control information symbol. A frame may also include not only apreamble but also a postamble, which is a signal added at the rear endof the frame.

The encoders use low density parity check (LDPC) coding, turbo coding,etc., for example, as the error control coding scheme. The encoders mayalso use another coding scheme.

The transmission devices illustrated in FIG. 1, and FIG. 13 to FIG. 15include their respective interleavers, but may not include interleaversas described above. In such a case, the transmission device may input abit stream generated by each encoder directly into each mapper or mayperform a process different from interleaving on the bit stream beforeinputting it into each mapper. When the transmission device does notinclude any interleavers, the reception devices illustrated in FIG. 2,FIG. 7, and FIG. 16 to FIG. 19 may not include any deinterleavers.

The deinterleavers of the reception devices illustrated in FIG. 2, FIG.7, and FIG. 16 to FIG. 19 perform permutation on the basis of apermutation rule that is a reverse rule of the permutation rule used bythe transmission side, but may perform an operation different from suchpermutation. For example, each deinterleaver may input into thecorresponding decoder a plurality of bit likelihoods of a bit likelihoodstream generated by the corresponding demapper in the bit order requiredfor decoding performed by the decoder.

In the above description, although superposition coding and thevariation of superposition coding are applied to wireless transmission,but the present disclosure is not limited to the application to wirelesstransmission, and thus may be applied to wired transmission, opticaltransmission, etc. and also to storage into a recording medium. Afrequency band used for transmission is not limited to a radio-frequencyband, and thus may be a baseband.

“A plurality of” used in the present disclosure is synonymous with “twoor more.” Ordinal numbers such as first, second, and third may beremoved from the expressions, replaced by other wording, or newly addedas appropriate.

Note that the devices, methods, etc. according to the present disclosureare not limited to the respective embodiments, and thus allow forvarious modifications for implementation. For example, in theembodiments, the technology of the present disclosure is implemented asa communication device (transmission device or reception device), butthe technology of the present disclosure is not limited to this, andthus may be implemented as software used to execute a communicationmethod (transmission method or reception method) executed by suchcommunication device.

Also, two or more structural components of the transmission device orthe reception device may be integrated as a single structural component,and a single structural component may be divided into two or morestructural components. Also, the transmission device and the receptiondevice may form a single transmission/reception device. In such a case,a plurality of structural components of the same kind may be integratedinto a single structural component. For example, a transmission antennaand a reception antenna may be formed by a single antenna.

Also, for example, a process performed by a specified structuralcomponent may be performed by another structural component. The order ofperforming processes may be changed, and a plurality of processes may beperformed in parallel.

Note that a program for executing the above-described communicationmethod may be previously stored in a read only memory (ROM) to beexecuted by a central processing unit (CPU).

Moreover, the program for executing the above communication method maybe stored in a computer-readable recording medium. Such program storedin the recording medium may be recorded in a random access memory (RAM)in a computer so that the computer may execute the communication methodaccording to the program.

Note that each of the structural components according to theembodiments, etc. may be implemented as a large-scale integration (LSI),which is typically an integrated circuit. The structural components maytake the form of individual chips, or one or more or all of thestructural components according to the embodiments may be encapsulatedinto a single chip. Although LSI is illustrated here as an example, suchchips may be referred to as integrated circuits (ICs), system LSIs,super LSIs, or ultra LSIs, depending on their degree of integration.

The ICs are not limited to LSIs. Each of the structural components thusmay be implemented as a dedicated circuit or a general-purposeprocessor. A field programmable gate array (FPGA) that allows forprogramming after the manufacture of an LSI, or a reconfigurableprocessor that allows for reconfiguration of the connection and thesettings of circuit cells inside an LSI may be employed.

Furthermore, when the progress in a semiconductor technology or anotherderivative technology results in a new IC technology that replaces LSI,such new technology may off course be employed to integrate the devicesor some of their structural components according to the embodiments. Forexample, adaptation to biotechnology is possible.

The present disclosure is widely applicable to radio systems fortransmitting different modulated signals (multiplexed signals) fromdifferent antennas. The present disclosure is also applicable tomultiple-input multiple-output (MIMO) transmission in a wiredcommunication system that includes a plurality of transmission points.Examples of such wired communication system include a power linecommunication (PLC) system, an optical communication system, and adigital subscriber line (DSL) system.

Although only some exemplary embodiments of the present disclosure havebeen described in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of the present disclosure. Accordingly, all suchmodifications are intended to be included within the scope of thepresent disclosure.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to a wireless communication systemand a broadcasting system, etc. The present disclosure is widelyapplicable to a system for multiplexing a plurality of data series bysuperposition coding.

The present disclosure is also applicable to a wired communicationsystem, etc. such as a power line communication (PLC) system, an opticalcommunication system, and a digital subscriber line (DSL) system. Thepresent disclosure is further applicable to a storage system, etc. forrecording data into a recording medium such as an optical disk and amagnetic disk.

What is claimed is:
 1. A reception device that receives a multiplexedsignal into which a plurality of data series have been multiplexed bysuperposition coding, and derives the plurality of data series from themultiplexed signal, the plurality of data series including a first dataseries in a first layer and a second data series in a second layer, thereception device comprising: a receiver that receives the multiplexedsignal; a first demapper that demaps the multiplexed signal, with asecond modulated symbol stream of the second data series being includedin the multiplexed signal as an undefined signal component, to generatea first bit likelihood stream of the first data series; a seconddemapper that demaps the multiplexed signal, with a first modulatedsymbol stream of the first data series being included in the multiplexedsignal as an undefined signal component, to generate a second bitlikelihood stream of the second data series; a first decoder thatperforms error control decoding on the first bit likelihood stream toderive the first data series; and a second decoder that performs errorcontrol decoding on the second bit likelihood stream to derive thesecond data series.
 2. The reception device according to claim 1,wherein the multiplexed signal received by the receiver is a signal onwhich the first modulated symbol stream and the second modulated symbolstream are superposed at a predetermined amplitude ratio, and in which apolarity of a real part and a polarity of an imaginary part of eachmodulated symbol in the second modulated symbol stream are controlled inaccordance with the first modulated symbol stream, the first modulatedsymbol stream being generated by mapping a first bit stream of the firstdata series, the second modulated symbol stream being generated bymapping a second bit stream of the second data series.
 3. The receptiondevice according to claim 2, wherein the multiplexed signal received bythe receiver is a signal on which a first modulated symbol in the firstmodulated symbol stream and a second modulated symbol in the secondmodulated symbol stream are superposed, and in which the polarity of thereal part of the second modulated symbol is subjected to a reversal whena real part of the first modulated symbol satisfies a predetermined realpart condition and the polarity of the imaginary part of the secondmodulated symbol is subjected to a reversal when an imaginary part ofthe first modulated symbol satisfies a predetermined imaginary partcondition.
 4. The reception device according to claim 3, wherein thesecond demapper demaps the multiplexed signal to generate the second bitlikelihood stream, based on a superposition constellation that is acombination of a first constellation used to map the first bit streamand a second constellation used to map the second bit stream, and thatreflects the reversal of the polarity of the real part of the secondmodulated symbol and the reversal of the polarity of the imaginary partof the second modulated symbol.
 5. The reception device according toclaim 1, further comprising: an encoder that performs error controlcoding on the first data series derived by the first decoder to generatea first bit stream of the first data series; a mapper that maps thefirst bit stream to generate the first modulated symbol stream; adelayer that delays the multiplexed signal received by the receiver fora predetermined time length; and a subtractor that subtracts the firstmodulated symbol stream from the multiplexed signal delayed by thedelayer, wherein the second demapper demaps the multiplexed signal, withthe first modulated symbol stream being included in the multiplexedsignal as an undefined signal component, to generate the second bitlikelihood stream, when a signal-to-noise ratio of the multiplexedsignal satisfies a predetermined requirement, and demaps the multiplexedsignal from which the first modulated symbol stream has been subtractedto generate the second bit likelihood stream, when the signal-to-noiseratio of the multiplexed signal fails to satisfy the predeterminedrequirement.
 6. A reception method of receiving a multiplexed signalinto which a plurality of data series have been multiplexed bysuperposition coding, and deriving the plurality of data series from themultiplexed signal, the plurality of data series including a first dataseries in a first layer and a second data series in a second layer, thereception method comprising: receiving the multiplexed signal; demappingthe multiplexed signal, with a second modulated symbol stream of thesecond data series being included in the multiplexed signal as anundefined signal component, to generate a first bit likelihood stream ofthe first data series; demapping the multiplexed signal, with a firstmodulated symbol stream of the first data series being included in themultiplexed signal as an undefined signal component, to generate asecond bit likelihood stream of the second data series; performing errorcontrol decoding on the first bit likelihood stream to derive the firstdata series; and performing error control decoding on the second bitlikelihood stream to derive the second data series.
 7. The receptionmethod according to claim 6, wherein the multiplexed signal is a signalon which the first modulated symbol stream and the second modulatedsymbol stream are superposed at a predetermined amplitude ratio, and inwhich a polarity of a real part and a polarity of an imaginary part ofeach modulated symbol in the second modulated symbol stream arecontrolled in accordance with the first modulated symbol stream, thefirst modulated symbol stream being generated by mapping a first bitstream of the first data series, the second modulated symbol streambeing generated by mapping a second bit stream of the second dataseries.
 8. The reception method according to claim 7, wherein themultiplexed signal is a signal on which a first modulated symbol in thefirst modulated symbol stream and a second modulated symbol in thesecond modulated symbol stream are superposed, and in which the polarityof the real part of the second modulated symbol is subjected to areversal when a real part of the first modulated symbol satisfies apredetermined real part condition and the polarity of the imaginary partof the second modulated symbol is subjected to a reversal when animaginary part of the first modulated symbol satisfies a predeterminedimaginary part condition.
 9. The reception method according to claim 8,wherein in the generating of the second bit likelihood stream, themultiplexed signal is demapped to generate the second bit likelihoodstream, based on a superposition constellation that is a combination ofa first constellation used to map the first bit stream and a secondconstellation used to map the second bit stream, and that reflects thereversal of the polarity of the real part of the second modulated symboland the reversal of the polarity of the imaginary part of the secondmodulated symbol.
 10. The reception method according to claim 6, furthercomprising: performing error control coding on the first data seriesthat has been derived to generate a first bit stream of the first dataseries; mapping the first bit stream to generate the first modulatedsymbol stream; delaying the multiplexed signal that has been receivedfor a predetermined time length; and subtracting the first modulatedsymbol stream from the multiplexed signal that has been delayed, whereinin the generating of the second bit likelihood stream, the multiplexedsignal is demapped, with the first modulated symbol stream beingincluded in the multiplexed signal as an undefined signal component, togenerate the second bit likelihood stream, when a signal-to-noise ratioof the multiplexed signal satisfies a predetermined requirement, and themultiplexed signal from which the first modulated symbol stream has beensubtracted is demapped to generate the second bit likelihood stream,when the signal-to-noise ratio of the multiplexed signal fails tosatisfy the predetermined requirement.